The Effects Of Speed Humps On Vehicles Engineering Essay

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Abstract

This project will examine the effects of speed humps on vehicles within the United Kingdom. Intensive investigation and reviews will be carried out on traffic calming measures used in the UK and a number of different aspects within the topic such as those currently in use and how improvements can be made to reducing traffic. The report also takes a close look at how speed bumps have affected commuters and its impact on the environment as a whole and businesses around the country.

As the number of vehicles on the roads increase faster than new roads that can be constructed, a serious problem has been created that is highly visible in urban and residential areas around the country. This problem is caused by fast driving motorist who do not take care on the road and it occurs on a daily basis. Conceding the fact that there are no single solutions to this problem and no quick fix, it is very important in assessing the success of the project. The understanding of why speed bumps were put in place on the road is a major factor in tackling the issue of speeding. To do this, time was invested in collecting data information from urban roads and residential roads in Islington and Hackney. This was very important as it helped me to provide an insight into how different motorist approach speed bumps and speed cameras, and what speed they approached the bumps and camera at different times of the day throughout the day.

Three major problems were identified with speed humps, the first being effectiveness of speed bumps. On residential roads the speed limit is 20mph. Although many motorist were at constant speeds of approximately 20mph, many vehicles had to alter their speed limit whilst travelling over the speed bumps as they are unaware of which bumps are too high of the required speed limit. Drivers, who did not take the precaution of slowing down, would result in them scraping underneath their vehicles. Motorist are unable to identify weather a bump is too high or weather a constant velocity can be applied.

The second problem was the damaged caused to vehicles when drivers make the wrong judgement of speed when approaching the speed bumps. Third being modern speed cameras on urban roads. Although they incorporate the latest in detection technology, the system were unable to provide efficient co-ordination of the direction of speeding vehicles. Vehicles speeding from the opposite side of the speed camera still get flashed, even though the motorist is aware that no potential speeding fines would occur as it's the opposite side. The result of the review is a concept which imbeds intelligence into the current traffic signalling system.

Introduction

Speed Bumps (sometimes called a sleeping policeman) are a traffic calming tool designed to slow traffic. A Speed Bump is a bump on a roadway that may be circular, parabolic, or sinusoidal, and it may have gaps near the curb to allow drainage. Speed bumps are widely used across the United Kingdom, and are gradually increasing on the roads year by year.

Speed Bump heights range from as little as 50 mm, to as much as 152 mm and they can vary in length from less than 300 mm to as much as 3x103mm. Speed Bumps longer than 3x103 mm are usually called speed humps, and they are often used to slow traffic in residential neighbourhoods. Some drivers could say that they prefer to go over these types of traffic calming tool as it is easier on the car.

Although Speed Bumps are very effective in keeping vehicle speed down, their use is sometimes controversial as they can cause noise and possibly vehicle damage. Poorly designed Speed Bumps are too tall, too sharp an angle for the expected speed and can be hard to negotiate in vehicles with low ground clearance, such as sports cars, even at very slow speeds. The driver can sometimes hear the Speed Bumps scrap the bottom of the car.

Project Aims

The aim of this project is to design an effective and efficient speed hump system that can be used in the United Kingdom. The design must be futuristic in its approach and incorporated a wide range of different technologies, both present and those in the development stage. These technologies must not only perform the role of slowing down vehicles but also reducing the effects on vehicles and to those who drive the vehicle. The speed hump design must be able to differentiate between high and low velocity and small and large vehicles i.e. (cars, buses, lorries). The dimensions of the hump must be within the UK regulations.

People tend to approach speed-bumps in one of three ways. They remain at their current speed and drive straight through without a care or thought for the car's undercarriage or suspension. They slow down to an appropriate speed and glide over the top. Or they slow down so much they cause drivers behind them to break. A new design will change the way drivers approach speed humps in general. The design must allow drivers who are travelling at the right speed limit to pass over the hump without difficulty but will remind drivers travelling above the limit to slow down by creating the same feeling that they get when passing over a speed-bump but without the usual speed-bump impact. (Jude Garvey, The Bumpfree Dynamic Speedbump gives drivers a smooth ride,2010)

The speed hump will be design to reward drivers who are travelling at the correct speed - by offering an almost unnoticeable pass. Internal cells within the speed bump will contain non-Newtonian Thixotropic fluids which will instantly react with the speed at which a driver makes contact with the speed-bump - immediately reminding them if they are going too fast.

for the speed hump to be effective, A double-layer bladder protection will help to ensure a long product life and allow the speed bump to be used in various conditions. if this is not done, the speed hump will not be durable and would need to be replaced regularly. this is not cost effective. The design of the hump is expected to be most useful in environments where speed needs to be kept at a safe level, for example hospitals, school zones, or where vehicles are entering and exiting with precious cargo or people onboard. It can be placed against a piece of shaped bitumen or be in a bolt down form of plastic. Made mostly from recycled rubber, the design will be textured and suited for the environment in which they are placed. (. (Jude Garvey, The Bumpfree Dynamic Speedbump gives drivers a smooth ride,2010)

Historical development

Traffic humps have been in existence in the UK since the early 1970s, but following criticism of the speed deterrents, lead to a new way of alternatives being developed. There are currently around 50,000 traffic humps on British roads today, which can be said to be a lot. however, there are a lot of vehicles on the road and if they were not there as a deterrent, there would have been a lot more accidents on the road due to drivers who do not follow the rules of the road.

The round-top hump can be said to be the most familiar in the hump family. The round-top was developed in the Netherlands and landed on British roads in the early seventies. Still the most common, the round-top hump is between 25mm and 100mm high and up to 3.7m long. (Dave Wilson, 2001 Inflatable rubber policeman gives drivers the hump)

To pass over speed bumps without causing any damage to the vehicle or causing discomfort to the driver and passengers, the driver must slow down almost to a complete stop. Speed humps are 76-100 mm high and 3.5 to 6.5 m long, therefore to avoid driver discomfort, the driver slows to a speed of 15-20 mph. Unlike speed bumps, at excessive speeds, the effects of speed humps are increased sometimes to the point of acting like a bump and jolting both the driver and their cargo. This causes discomfort to some drivers and could even lead to the damage of the products which they may have in their vehicle. There is nothing that they can do about it unless they have insurance for the products on board.

An example of a type of business that uses a vehicle all the time is removals. When having expensive and precious objects in the car, it is very important that time and care is taken over speed humps and speed bumps. Otherwise it could lead to damages which could affect the business and its reputation.

Location

The first speed hump in a series should be placed 15-60 meters from a small radius curve or stop signs assuring that vehicles are not approaching at high speeds. If installed on a street with a significant grade line, the first hump in a series should be placed at the top of the grade.

Research has shown that speed humps, when designed and installed properly, reduce vehicle speeds to 15-20 mph when travelling over speed humps and 25-30 mph in between properly spaced speed humps. When travelling over a speed hump, the vehicle experiences a gentle rocking motion that increases with speed. This enables the speed humps to be self-enforced because the vehicle occupants will experience discomfort when passing over a hump at higher speeds and a jolting when passing over at excessive speeds. (Duane E. Smith, P.E.

Karen L. Giese, 1997, effects of speed humps)

Although speed humps have been proven to be effective at reducing speeds, they also come with their own drawbacks. Installed speed humps have actually been removed in response to resident complaints. The major complaints have been aesthetics of having speed humps and the increased noise level at each hump although the net noise change throughout the controlled strip is insignificant. Speed humps are not the best thing to have own ones road. Also if people are not happy, the council have to hear the complaints of the residents. It would not be nice to be living on a road where you can hear cars going over speed humps and scratching the humps as well as their car. It is not aesthetically pleasing when you leave your front door and see scratches on your road.

Although they are the most important group, more than just the residents are affected by the installation of speed humps. Other groups such as emergency service providers, street maintenance providers, school districts, transit operators, refuse collection agencies will be affected and should, therefore, be informed and consulted concerning the installation of speed humps. Emergency providers may have casualties in their vehicles and going over the humps may affect the injuries which the casualties have. Especially if they are in life threatening situation, they may need to move as far as possible.

CHAPTER 1 - REVIEW OF TRAFFIC CALMING

The design used in modern speed humps is not as advanced as it should be although it has been around for many years. With not a fair amount of improvement in terms of design a constant review of the system is always required. Speed hump plays it toll with traffic and congestion and the effects are mostly visible at peak time. Traffic congestion has many side-effects and does not just impact on motorist. The impact of growing congestion can be felt by businesses, local councils and mostly the environment.

Huge efforts are being made to ease traffic congestion in the United Kingdom and where introducing congestion charges, building new roads and improving the public transport are all viable solutions. Recent studies have shown that the general public prefers to own their own form of transport i.e. car as current public transport systems are unreliable. Building new roads is very costly and is not an option in major cities, and although congestion charges have seen a decrease in the amount of motorist on the roads in central London, traffic jams is still a regular occurrence at peak times.

Although forecasted figures shows the road traffic will rise in coming years. My project aims to comprehensively review the current speed humps system in the UK and to develop accordingly, a system that increases efficiency and maximise the flow of traffic as well as reducing impact. My project will also form a comprehensive review of congestion, looking at how traffic builds up at speed humps.

Types of speed hump currently used.

The flat-topped hump

This squarer version became fashionable in 1990 when traffic humps became regulated by the Highways (Road Humps) Regulations Act. Between 25mm and 100mm high and a minimum length of 2.5 m the optimum angle of tapered sides is a gradient of 1 in 4.

Thumps

Thumps are hard, triangular, thermoplastic strips approximately 37mm high and 900mm wide.

Speed cushions

Speed cushions are rectangular humps which laid across roads in twos or threes. Cushions are wide enough to slow cars but not buses and emergency vehicles.

Rumble strips

Not really a traffic calming measure, more a warning to drivers of something ahead.

Chicanes

Is a single lane sections and road markings represent a more recent attempt to slow down speeding motorists and modify the original traffic hump into a more comfortable disruption.

Congestion

Traffic and congestion caused by speed hump is a problematic condition on road networks that restricts the flow of traffic to extremely slow speeds. The problem occurs as the volume of vehicles increase to within close proximity of maximum the road network capacity. Traffic condition can be characterise by a number of different factors, namely increase queuing, increase journey time and relatively slow speeds. This problem is a regular occurrence in modern urban cities, where the demand is at its highest. The demand in these areas is such that the interaction between vehicles causes the average speed of traffic to fall noticeably.

Figure 1 (UK figures for road traffic) [i] 

Figure 1.2 (Graph showing the trend of car ownership in the UK) [ii] 

The level of traffic congestion in the United Kingdom is considered to be one of the worse in whole of Europe. More worrying is the fact that it continues to get worse year after year. The increase rate of new vehicles on the road is considered to be unsustainable, as the increase rate is faster than the rate of which new road infrastructure can be constructed. The issue is a long term one, the solution to which cannot be seen due to lack of feasible measures to combat or event control the problem. It has already been conceded that it is infeasible to match a roadwork infrastructure program to the unconstrained inclination of current and future traffic growth.

Figure 1.3 (Central Forecast Figures Made By the Department Of Transport for the UK) [iii] 

Figure 1.4 (Graph Shows Trend of the Number Vehicles Licensed Each Year in the UK) [iv] 

causes of congestion

A major issue in modern times is travel efficiency. Speed humps clearly make travel less efficient. A particular problem is traffic that has diverted to avoid a scheme of humps. Such diversions tend to exacerbate congestion on through routes where there are less likely to be humps.

Apart from the rapid increase in the number of vehicles on the road, there are several other factors contributing to the problem. Some of which are can be solved with time, while some are control by financial constraint. Other solutions are not considered to be feasible in terms of the level resources needed as they involve relocating home owners and local businesses. More often than not traffic congestion due to speed bump but propagates from junction and roundabouts.

environmental impact

Humps cause wider variations in vehicle speeds, with many vehicles slowing to a crawl to negotiate each hump. A natural consequence of a wider variation in speed with more acceleration and more braking is that more fuel will be used. If more fuel is used then more pollution is created. If traffic speeds are reduced journey times will increase and a baseline level of pollution will be delivered for longer periods.

The impact on health via polluted air the most common, as vehicles emissions contributes up to 40% of the total amount toxic gases emitted each year. Emitting a wide a variety harmful gases, such as carbon monoxide, nitrous oxide and other bi-products of partial contribution. Humans as well as animals are directly affected by the immediate environment and being exposed to polluted air on a regular basis can lead to short and long term health related illnesses such as lung decease.

economical impact

Estate agents say there has been a decrease in property value due to speed humps, many potential buyers who notice many speed humps within the neighbourhood are less welling to purchases the property as they feel that speed hump make the neighbourhood unattractive. Different types of businesses are affected in different ways, business that relies on delivery of goods looses out as deliveries arrives late, causes delays in the time products can be process and put out shop floors. Late deliveries increase shift duration adding extra cost to employee's wages.

A BUS operator says the increasing number of speed humps in the town is costing the firm £500 a month in repairs.

Bosses at the Stagecoach Midland Red depot, say their vehicles are being repeatedly damaged by the humps. Fuel tanks have been knocked off buses, causing diesel to spill across the road, something which the company believes could leave them liable to bills running into thousands of pounds if it were to cause an accident.

Engineering staff understand the speed reduction measures installed by Warwickshire County Council need to be taken but feel cameras would be more beneficial.

Mick Merriman, engineering manager for the firm, said: "The spate of damage from road humps is an on-going cost. Speed cameras would be preferable, certainly as far as our buses are concerned.

"The humps also cause discomfort to passengers and drivers, who would be pleased to see the end of them."

Manager Bill Breen added: "We've written to the county council about this issue and our operations director is in talks with the council."

Dec 18 2001 Coventry Evening Telegraph

www.coventrytelegraph.net/new

Experts have estimated the annual maintenance cost of speed humps to road to be in the region of 1.3 million pounds, the majority of which is related to repair cost and maintenance. There are also indirect costs of speed humps associated with the effectiveness of logistical operations at either ends of the transportation process. These additional costs are estimated to be very significant however they are considered to be intangible variables like additional scheduling costs and journey reliability are very difficult to quantify. Figure 1.5 is a photograph taken by myself, which illustrates a speed hump under different weather condition and vehicle weight. A large quantity of speed humps in the UK are damaged, where one of the major reasons is weather conditions; whenever rain falls on to speed humps creaks that have been created by frequent hard impact on the hump, then get filled with water, as temperature decreases this water then turn into ice, causing the hump become fatigue, eventually the creak will spread and can cause the hump to completely separate in this case a huge portion of the hump has been worn away, as its internal properties has weaken due to separation vehicles have continuously driven over this weak area and has eventually got to this stage of completely deterioration on one side of the hump.

C:\Users\Public\Pictures\Speed bump\DSC01888.JPG

Figure 1.5 (Picture Shows damaged speed hump due to weather change and vehicle impact.)

measures to reduce congestion

Tackling congestion is very difficult both in theory and in practice. Theoretical concepts are very difficult to implement as they can sometimes damage public relation which can lead to protests. These concepts sometimes derive from models and computer simulated data and analysis which does not always reflect the unpredictability of the real world situation. Since congestion is judged on cost, ample efforts have been concentrated on reducing the annual cost. Some efforts tackle the problem head on by addressing the main issues where as other aim at charging motorist to balance the annual cost. Congestion charge is one such method that aims to cut congestion by cutting the cost. The cost of which is worth approximately 6 billion pounds per year.

A large proportion current and futuristic solution to ease traffic congestion, are aimed directly at reducing the number of vehicles on the roads. The focus of major campaigns has been on persuading motorist to utilise other forms of transport. The difficulty in this is that substitutes to the car are not considered to be feasible as public transport one of the main and only substitute is not very reliable. For this to be seen as a suitable substitute there must be an increase in arrival and departure times for both buses and trains. The service must also be reliable cost effective to customers and operators alike. Two areas that have seen reasonable levels of success and support are cycling for those making short journeys and transferring road freight to the rail. The combined effects of numerous supportive complementary solutions represent the best way forward in the short term and could slow the rise of road traffic y 25% - 45%.

CHAPTER 3 - RESULTS AND FINDINGS

Traffic Data Gathering

Gathering real time data is vital in understanding the flow of vehicles passing over speed humps, on residential road and urban roads. The data will help to understanding and identifying the factors affecting speed humps in more details, such as time of the day and days of the week. Understanding how the speed bump deals with fluctuating weight and speed levels at peak and off-peak times also provide an insight into how efficient the design is. The main reason for conducting investigation in this form is mainly to identify flaws in operation if any.

Hump profiles

The dimensions of the profiles chosen for evaluation are shown in Table 1. The five hump profiles used in the trials included three profiles not commonly used: a 3.7m long sinusoidal profile, a 5m long round-top profile and an 8m long flat-top with sinusoidal ramps. Two standard profiles were included for comparison: a 3.7m long round-top profile and an 8m long flat-top hump with straight ramps. All the hump profiles were 75 mm high.

Fig 2: Profile dimensions

Vehicles tested

A range of vehicles was used in the trials to assess discomfort, noise and ground borne vibrations. These included five different bicycle types, a small, medium and large car, five different buses, including a low floor bus, three different goods vehicles with steel or air suspension, a fire appliance and three different ambulances.

Figure 2.1 Unladen cyclists

Figure 2.2 Motorcycles - combined results from small, medium and large motor cycles

Figure 2.3 Minibus (Optare City Pacer all passengers sitting)

Figure 2.4 large single-deck buses (Optare Low Rider - Low floor bus)

Figure 2.5 Double-deck buses (Optare Spectra)

Discussion & Analasys Of Resusts

For cyclists, motor cyclists and all occupants of cars, buses, goods vehicles and emergency service vehicles, a subjective assessment of discomfort (DR) was made on a scale 0 to 6. A discomfort rating of"0" means comfortable, and "6" very uncomfortable. Additionally, for all but cyclists and motor cyclists, an accelerometer was used. For each of the tests, this measured the vertical acceleration experienced by one occupant in every vehicle.

Cyclists

In promoting an increase in cycling it is important that, as far as possible, cyclists are offered a comfortable ride. Figure 1 shows the average discomfort ratings for unladen cyclists crossing the various hump profiles at 10 mph and 20 mph. similar results were found for laden cyclists (5kg load).

It can be seen from Figure 1 that cyclists experienced the most discomfort when crossing the flat-top humps and that the 5m long round-top profile gave the least discomfort. This profile also gave the least discomfort to the car occupants but its use would be likely to result in higher car speeds than with the other hump profiles. For humps of a similar length (3.7m), the sinusoidal hump was more comfortable for the cyclists than the round-top profile.

Motor cyclists

Stability and comfort are important to motorcyclists, but where motorcyclists report discomfort crossing road humps; this may be due to inappropriate speeds. The tests were made using carefully controlled speeds, judged to be appropriate to the circumstances. Average discomfort ratings (DR) for motorcyclists are shown in Figure 2.2.

For motor cyclists, there was less difference in the discomfort experienced between the hump profiles than for the cyclists. However, the 5m round-top hump was clearly the most comfortable and the flat-top humps were the most uncomfortable.

Buses

The average discomfort rating experienced by passengers sitting in a minibus, a low floor single deck bus and a double-deck bus is shown in Figures 2.3, 2.4 and 2.5. These illustrate how a small change in speed can lead to a large increase in discomfort, particularly in minibuses and double-deck buses.

There was less variation in the discomfort experienced when crossing the different profiles in the double-deck bus than for other bus types. For all three bus types at speeds of 15 mph or less, passengers generally experienced less discomfort with the round-top and sinusoidal profiles than with the flat-top profiles. At speeds above 15 mph, general levels of discomfort were unacceptable for all the profiles tested.

Low floor buses

Low floor buses are of particular interest, as it has been claimed that these vehicles are more susceptible to grounding when passing over road humps. In fact, the clearance of low floor buses above the carriageway was found to be very similar to that for other buses.

The main problem would seem to occur where there is a greater overhang at the front and/or rear of the vehicle. With the bus used (Optare low-rider) the track trials did not reveal any grounding problems with the 75mm height humps used, although the driver declined to cross the flat-top profiles at 25 mph because of concern about possible damage. As pointed out above, this speed would generally be considered unsuitable in terms of the discomfort likely to be experienced.

Noise

Light vehicles

For the passenger cars tested, the differences in the maximum A-weighted noise levels generated alongside the different profiles were relatively small, and were not likely to be of practical significance. Noise levels when crossing humps generally increased as the speed increased, and tended to be slightly less than that measured on a level surface. For light vehicles, maximum noise levels would not be expected to increase as a result of installing any of the profiles tested.

Double deck bus

The double deck bus also showed a general increase in the maximum noise level with increasing speed. There were differences, with the sinusoidal profile giving lower noise levels than the non-sinusoidal profiles.

The highest noise levels were measured alongside the flat-top (straight ramp) profile. All the profiles gave lower noise levels at typical crossing speeds than measurements taken next to the level surface, where speeds were higher.

Large Goods vehicles

At typical crossing speeds, the noise levels for goods vehicles tested were highest alongside the flat-top profiles. The noise levels for sinusoidal profiles were slightly lower than their non-sinusoidal equivalents. The 5m long round-top profile was similar to the3.7m round-top profile with respect to noise generation.

Large goods vehicles may have either air or steel spring suspension. The maximum noise levels generated along the hump profiles by the 38t articulated tipper vehicle with steel spring suspension were higher than the equivalent vehicle with air suspension.

For air suspension vehicles, the unladen state generated higher noise levels than the laden state, for all the profiles tested. For steel spring suspension vehicles, the difference between the laden and unladen states was less distinct: the sinusoidal profiles generated higher noise levels for the laden vehicle, and the 5m round-top profile and the flat-top profiles resulted in higher noise levels for the unladen vehicle

Ground-borne vibration

Levels of ground-borne vibration generated by light vehicles showed no distinct difference alongside the different profiles. For the double-deck bus, the highest vibration level obtained at typical crossing speeds was for them flat-top (straight ramp) profile. For heavy goods vehicles, the highest mean and maximum ground-borne vibration levels at typical crossing speeds were also at the flat-top (straight ramp) profile. The flat-top (sinusoidal ramps) was slightly less, and the round-top and sinusoidal profiles had significantly lower levels. Higher levels of vibration were noted for the heavy goods vehicles running unladen, than when loaded.

C:\Users\Public\Pictures\humps\HPIM0971.JPG

Discussion & Analasys Of Resusts

The charts bellow are constructed from data celected from speed humps on a residential road, the first of which looks at the link between number vehicles passig over speed hump at speccfic time intervals during the day. The second graph looks at the influence on traffic levels, which shows connection between the number of vehecles and the day of the week.

Figure 3

(Pie-Chart, Showing Variation of vehicle passing over speed humps In Relation To Time of Day)

From the pie-chart it is evident that there are two periods during the 12 hours traffic levels are high. This is to be expected as peak times in the United Kingdom are between 7 - 11am, and 3 - 7pm. These two periods highlight a high level of activity that can be attributed to morning an evening school runs as well as commuters travelling to and from work.

Figure 3.1 (Pyramid Chart, Showing Variation Traffic Level In Relation To Day of the Week)

From the tables of results and the chart is clear that traffic fluctuate for reasons already stated. There are several other factors affecting the flow of traffic; however these variables cannot equated for in the data collection. Variables such as accidents and special events like football matches can also affect these figures. Road works is another of those variables that cannot be accounted for and can affect the figures. It is unclear of the role played by the weather on the figures as the weather can affect traffic in two different ways. Bad weather causing difficult driving condition can reduce traffic as motorist can decide not to travel if the journey is compulsory. Conversely it can also increase queuing as the average speed falls there by affecting traffic. Commuters cycling to and from work can also be affected prompting the switch from bicycle to car.

CHAPTER 4 - PROPOSAL & CALCULATIONS

Discussion & Analasys Of Resusts

The charts bellow are constructed from data celected from the T-junction, the first of which looks at the link between number vehicles passig through thejuction at speccfic time intervals during the day. The second graph looks at the other that has an influence on traffic levels, whic shows connection between the number of vehecles and the day of the week.

Figure 3.3 (Pie-Chart, Showing Variation Traffic Level In Relation To Time of Day)

From the pie-chart it is evident that there are two periods during the 12 hours traffic levels are high. This is to be expected as peak times in the United Kingdom are between 7 - 11am, and 3 - 7pm. These two periods highlight a high level of activity that can be attributed to morning an evening school runs as well as commuters travelling to and from work.

Figure 3.4 (Pyramid Chart, Showing Variation Traffic Level In Relation To Day of the Week)

From the tables of results and the chart is clear that traffic fluctuate for reasons already stated. There are several other factors affecting the flow of traffic; however these variables cannot equated for in the data collection. Variables such as accidents and special events like football matches can also affect these figures. Road works is another of those variables that cannot be accounted for and can affect the figures. It is unclear of the role played by the weather on the figures as the weather can affect traffic in two different ways. Bad weather causing difficult driving condition can reduce traffic as motorist can decide not to travel if the journey is compulsory. Conversely it can also increase queuing as the average speed falls there by affecting traffic. Commuters cycling to and from work can also be affected prompting the switch from bicycle to car.

The majority of traffic flowing through the intersection is highest in the weekday peak time periods (7 - 11am and 3 - 7pm). The highest levels of congestion occur on dual carriageway roads in the peak periods, while there is little congestion on motorways or dual carriageways in the intervening off-peak period. These patterns are highlighted by tables and in the charts above.

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