Widcombe Parade Survey: Traffic Management

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Table of Contents

Introduction
Data collection (trip generation)
Trip distribution
Traffic assignment
Response to Questions
Constraints
Comparison of the two options
Conclusion
References

Introduction

The study area of Widcombe is a district of Bath, to the south-east of the city center. The Kennet and Avon Canal meets the River Avon in Widcombe. The Residents of Widcombe have proposed closure of the Widcombe parade through traffic, and to divert it to Rossiter road. This road runs alongside the river, and immediately to the north of Widcombe Parade. Widcombe Parade is a one-way road taking traffic east to west. Rossiter Road is currently a one-way road west to east, built originally as a bypass to Widcombe parade. The Widcombe Residents Association and The Bath and North East Somerset Council have championed this proposal. These associations monitor planning applications that affect Bath as a whole. The removal of A36 traffic from Claverton Street has been the Association’s main campaign. Several plans have failed previously. They aim to preserve the environment and ways that give Widcombe its character. This proposal would mean that Rossiter road would have to become two-way. This will restrict the shopping street to carrying only local traffic and traffic off the A36 that has some business in Widcombe. At present, the two roads form part of the principal east-west route through Bath. Widcombe is also the focus of a number of roads that serve the south of the city, notably Widcombe Hill, Prior Park Road, and Lyncombe Hill. Widcombe and its environs are economically active. It is home to several companies, the Somerdale Factory, theatres, colleges, and tourism. Moreover, Widcombe has many listed and registered buildings. This means they are of cultural and historical value and should be preserved. The through traffic includes people traveling to work, heavy goods vehicles and other vehicles passing through Bath, and local bus services. This heavy traffic flow results in considerable congestion on Widcombe Parade all day.

There are both traffic and environmental reasons for implementing this scheme. Widcombe Parade contains shops that serve the local community, specialist shops that serve a wider catchment, and it has a number of well-known restaurants and pubs. It also has local services including a doctors’ surgery and two dentists and there is a resident population. The two functions of the principal traffic route and local shopping center are in direct conflict, Hence the study to resolve it. According to The Widcombe Association (2003) in conjunction with B&NES prepared a sustainability impact assessment in 2003. The report raised many issues of concern from the residents. There were personal safety concerns raised by the residents over the dangerous crossings and the vehicles’ priority over pedestrians and cyclists. There were also concerns over traffic noise, air pollution, and damage to buildings. Shopper attitudes indicate that they mostly regarded the parade as unpleasant and not user-friendly. They also considered the road to have divided the community in two. The inconvenience of parking on the parade was also a key complaint. Many residents were of the opinion that a reduction of speed and volume of traffic would improve many of these issues. The proposed scheme by the association would, therefore, extend beyond traffic management, to improve the life quality of the residents, the aesthetics of the area, and the business of the parade. The resultant air pollution on the parade is also a key complaint from the residents. At peak times, the air gets noxious as a result of all the exhaust fumes released by the vehicles. It affects the businesses and is liable to affect the health of people working on the parade.

Data collection (trip generation)

According to Salter (1989), traffic planning at any level requires the actual conditions to be understood. This entails the determination of the vehicle and pedestrian numbers (p.183). Traffic counts yielded the data. The Widcombe survey on traffic flow and content took two days. Wednesday 3rd and Thursday 4th of November 2010. It covered all the roads leading into Widcombe as well as on Widcombe Parade and Rossiter road. The survey determined the traffic flows at critical times of the day and identified the vehicles by class. There are four survey points:

A – Pulteney Road
B – Widcombe Hill
C – Prior Park Road
D – Claverton Street and Rossiter Road

For the purposes of this survey, Lyncombe Hill is not considered. The survey traffic tally took place three times every day: morning peak, midday, and evening peak. The output of the survey was in vehicles. The survey team utilized hand counters that were particularly instrumental in avoiding tallying errors. High-visibility jackets enhanced safety during the exercise. There were two counters at every survey point. Counters minimized human error by dealing with traffic in one direction only. A spreadsheet aided the recording and conversion of the vehicle tally to passenger car units (pcu). A pcu is essentially the effect that a mode of transport has on various traffic factors such as headway, speed, and density, compared to a single car. The data collected is in the appendix, both in actual vehicle count and pcu.

Trip distribution

According to Hensher (2007), “trip distribution is the second in the traditional four-step transportation forecasting model. In this step, trip makers origins and destinations match to display the number of trips going from each origin to each destination” (p.18). Black (2007) says that “a distribution model generates a new O-D trip matrix to reflect new trips in the future made by changes various demographic factors so as to reflect changes in people’s choice of destination” (p.72). Their application is in predicting the origin-destination travel pattern and producing a trip matrix. This is employed in an assignment model or included in a model for choice of mode. The trip matrix is subject to change due to improvements in the highway network or new developments. The distribution model applies these changes in order to generate a new trip matrix.

There are four traffic zones corresponding to the tally points. Zones A, B, C, and D refer to the regions of origin or destination of the vehicles passing through the corresponding checkpoints. According to O’Flaherty (1997), “Models are simplified representations of reality which can be used to explore the consequences of particular policies or strategies” (p.). Also, Ortuzar (1996) notes that “a model can be defined as a simplified representation of a part of the real world – the system of interest – which concentrates on certain elements considered important for its analysis from a particular point of view” (p.13). Vaughan (1987) described travel distribution models as urban planning models that consider the distribution of land use and land use over the city with analysis accurate to a certain area (p.3). Trip distribution entailed using a simple model: The Furness Model. According to Erlander and Stewart (1990), “this is the simplest model for deriving the future year trip matrix from the base year traffic” (p.8). The Furness model converges quickly. This model also works with cells of zero or negative values. It is commonly utilized in transportation network modeling. However, less often, it is applied in more complex and demanding distribution models. It has two weaknesses. Firstly, if a cell in the matrix is zero, it will not change despite factoring. Secondly, it is insensitive to changes in the system of transport. The Furness analysis and the result are in the appendix.

Traffic assignment

Modern transportation networks are intensively used and are mostly congested to varying degrees, especially in urban areas. According to McLean (1989), “Traffic assignment in a network considers a demand between locations and the transport supply of the network” (p.33). In order to successfully decongest the Widcombe parade, it is necessary to reassign some of its traffic to other routes. This traffic is carried by a newly introduced lane on the A36 which will convert it to a two-lane road. From the Furness analysis in appendix 3, it can be seen that the highest amount of through traffic recorded was 270pcu. This is the traffic volume that will now be assigned to the new two-way road, in addition to the 1251pcu it is already transferring. The total traffic flow will, therefore, be 1521pcu. The road design should take care of this flow. The rest of the traffic from Prior Park Road and Widcombe Hill Road will be flowing in an easterly direction thereby entirely bypassing the new road. The traffic analyses employed a growth factor of one. Rossiter Road is the only road that changes significantly. With the new easterly flow of traffic on Widcombe Street, the junctions will need to be redesigned to accommodate the changes. There will be new points of conflict introduced. The traffic lights will also have an impact on the capacity of the roads.

From the traffic analysis, it can be seen that the problem facing Widcombe is congestion. There is a very high flow of traffic in the peak hours which all pass through the parade. It is necessary to divert some of this traffic away from the parade to reduce congestion. The proposed two-way system for Rossiter Road is a viable solution. The peak traffic observed is mainly on the east-west roads. Shifting the surplus traffic to a new east-west alignment will reduce congestion. This will happen with minimum interruption to traffic flows. There will, however, be a number of traffic conflicts, mostly at the roundabouts. Resolving these conflicts will require an extensive and ingenious system of pavement markings and vehicle stream isolation. This will be particularly beneficial on the junctions on Rossiter Road because they will be bearing high-speed traffic. An environmental problem may arise in the expansion of the bridge over the canal. The expansion is to cater for the new widened two-way highway. This can, however, be solved by careful audit and mitigation.

Response to Questions

Noise pollution is a leading source of concern for the residents. Various types of vehicular traffic cause noise pollution. The need for hooting, arising from congestion, exacerbates the situation. These conflicts cause excessive hooting. The heavy flow of vehicles on the parade has rendered the air noxious with the exhaust gases. These gases are injurious to the people who inhale them. The effect of these gases is worse for residents who work on the parade, because of all-day exposure. These emissions are worse when vehicles are stationary or slowly driven. They can also contribute to low visibility due to smog. The vibrations caused by the heavy goods vehicles can cause serious damage to the buildings along the parade, some listed buildings. The smoke from the exhaust also irreversibly discolors the buildings.

Constraints

The solution faces financial constraints because of cost-effectiveness requirements in its design. The location is also highly developed so the solution faces space constraints. The new roads can deviate from their present course only marginally. Most importantly is the insufficient space for creating a right turn from Rossiter road as a two-way road. The limited space available on the bridge will produce an engineering challenge. This means that the bridge will require widening so as to accommodate the two-way traffic. This challenge will also affect the cost constraints of the project, especially if requiring an entirely new bridge. Extra space will also be required in backing up to the Churchill Roundabout. The required solution should also be aesthetically pleasing so as not to render the shopping area around the parade unpleasant to the eye. There will also be some traffic movement constraints. This especially faces traffic backing up the hill to Churchill roundabout. The control of the limited traffic through Claverton Street will also pose a challenge. Lastly, a significant traffic direction challenge will be in establishing the layout of the Widcombe Hill and Prior Parker Road junction.

Comparison of the two options

Two options are under consideration by the Widcombe residents Association and The Bath and North East Somerset Council. Both options one and two require the conversion of Rossiter Road into a two-way road that will carry through traffic. With the through traffic retained on the Rossiter Road, Claverton Road will be reserved for local traffic and traffic diverting from the A36 via the Pulteney Road to engage in Shopping on the parade. The key difference between the two options is the reversal of traffic on Claverton Road. Presently, traffic flows along Claverton in a Westerly direction. Option one retains the westerly traffic direction. Option two reverses the flow of traffic to an easterly direction. As a result of this change in the direction of flow between the two options, there is a change of design in traffic separation and direction at the Pulteney Roan and Rossiter Road roundabout. In option one, the through traffic traveling towards Widcombe diverts to the right at the roundabout to keep on the two-way Rossiter Road. In option two, however, traffic wishing to join Rossiter or Pulteney Roads takes a left turn at the junction. This difference in the direction of flow on Claverton Road also brings about substantial changes in the direction of the flow of traffic at its two main junctions. These are the Claverton-Widcombe Hill-Prior park junction and the Claverton Road–Rossiter Road junction. Both upgrade options face the challenge of correctly configuring these two junctions so as not to affect traffic flow on the tributary streets negatively. Both options are superior compared to the existing situation. The existing situation with its myriad problems does not deliver the standard expected by the residents of Widcombe. It has turned the Widcombe parade into an excessively busy and noisy thoroughfare. Therefore, the baseline situation should not be considered as an option if the residents of Widcombe are to have their way. In terms of environmental impact, both option one and option two present the same solutions. They are both capable of easing the various forms of pollution affecting the Widcombe parade. This alleviation is a realization of the assignment of traffic to the new network that includes a two-lane Rossiter Road (A36). During peak hours, the traffic headed eastwards exceeds the traffic flowing westwards towards the general direction of Bristol. It is, therefore, prudent to select the option that allows easy merging and weaving of traffic headed in an easterly direction. This option is option two. A sizeable portion of the traffic issuing from the South of Widcombe via Prior Park Road and Widcombe Hill Road travels east through Pulteney road. It is, therefore, easier for them to access this road in option two than in option one. Under option one; these commuters have to make a long journey through the Claverton-Rossiter junction, experiencing more points of conflict than in option two. Option two is, therefore, superior to option one in terms of traffic flow. An easterly traffic flow as in Case two also has another advantage. The traffic from the southern tributaries; Prior Park Road and Widcombe Hill Road, do not need to use the newly created lane if traveling east to Pulteney Road. This means a reduction in the capacity requirement for the new lane. Consequently, the capital outlay is also reduced. This also means that the widening of the canal bridge will be to a lesser extent.

To a great extent, the scheme cannot be addressed independently of the wider transport issues in Bath. The issue under consideration in Widcombe involves changing the amount of traffic that goes through the parade. While it only requires a small diversion of the major traffic, there is considerable traffic change planned in the larger Bath area. These existing problems and their planned solutions will affect this project. For instance, The Council has plans that will effectively reduce the number of all types of cars on the roads in favor of pedestrians and cyclists. The project should, therefore, consider any anticipated changes that will significantly influence the flow of traffic in the whole of Bath. In the event that these factors in the larger Bath area are ignored, problems may arise at a later stage, well after the project’s completion.

The wider Bath area experiences a number of Traffic problems. Key among them is crippling congestion during peak hours. These conditions are worsening. According to The Bath and North East Somerset Councils Website (2010), new figures show that the number of vehicles traveling through the Bath city center is likely to increase by up to 14% in the next decade. The number of commuters is also exceptionally high at 27,000, and it causes an estimated loss to the economy of fifty million pounds annually. Vehicles in peak traffic spend as much as a fifth of the travel time at a standstill. The Council is planning substantial improvements across the whole area to improve traffic flow. Some of the proposed solutions include better bus routes and rapid bus transit. They also plan to improve conditions for pedestrians and cyclists while cutting back on the number of private vehicles. There are also plans to set up a transshipment center to reduce the number of heavy goods vehicles on the roads.

The scheme will improve the current problems. In regard to the noise problem, the reduced traffic on the Widcombe parade will directly lead to reduced noise levels. The noise level reduction will be significant especially because the heavy goods vehicles that generate the most noise remain on Rossiter road. The majority of the traffic retained on Claverton Road will be local traffic. These residents are likely to be careful about the noise they generate. The noise levels will also be significantly reduced because of the low vehicle-cyclist-pedestrian conflicts. The conflicts are the main cause of hooting in the parade. With these conflicts drastically reduced, there will be a much lower incidence of hooting, hence less noise. The congestion problem will also be significantly reduced. Heavy goods vehicles, light goods vehicles, and any other through traffic that has no business in Widcombe will use the two-way A36. Local traffic and those vehicles with business in Widcombe will now have sufficient space to maneuver on the parade.

The parking problems will also be reduced. Fewer vehicles going through the parade imply a reduction in competition for the parking spaces. The local population will, therefore, benefit from the freed-up parking spaces when shopping or visiting the businesses on the parade. The project has the potential to worsen the situation in Widcombe, in a number of ways. For instance, the three roundabouts on Calverton Road will require significant redesign. If they are poorly designed or constructed, they may result in traffic congestion on the parade itself and the tributary roads. A poor junction design on the Widcombe Hill-Calverton Road-Prior Park Road may cause regular traffic backups on these tributary roads.

Conclusion

The traffic survey and subsequent analysis have revealed that the Widcombe parade is bearing a heavy traffic flow. This traffic flow is the cause of many problems facing the residents as they transact their affairs on the parade. The recommendation to change Rossiter Road on the A36 into a two-way road so as to alleviate congestion on the parade is sound. The parade remains open to local traffic and A36 traffic that diverts to shop. It is demonstrated that option two of the proposals, which includes the reversal of traffic flow is more suitable than option one. The capacity of the new highway lane has also been demonstrated to be manageable.

References

Black, J. (1981). Urban transport planning: theory and practice. Oxon, Taylor & Francis

Erlander, Sven and Stewart N. (1990). The gravity model in transportation analysis: theory and extensions. Leiden, VSP.

Hensher, David and Button, John K. (2000). Handbook of transport modelling. Bingley, Emerald Group Publishing.

McLean, J. (1989). Two-lane highway traffic operations: theory and practice. New York, NY, Gordon and Breach Science Publishers.

O’Flaherty, A. (1997) Transport planning and traffic engineering. London, Arnold.

Ortuzar, Juan et al. (2001). Modelling transport. Indianapolis, IN, John Wiley and Sons.

Salter, R. (1989). Highway traffic analysis and design. Michigan, Macmillan Education.

The Bath and North East Somerset Councils Website (2010). Better Public transport. Web.

The Widcombe Association (2003). Rossiter Road Campaign Key Reports. Web.

Vaughan, R. (1987). Urban spatial traffic patterns. Oxon, Taylor & Francis.

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