street design final submission

Cl318 Transport Engineering Gordon Best 201109204

Street Design Project- Individual Submission

The street which shall be studied and re-designed for this project is Shawlands Cross (fig. 1) in the Shawlands area of South Glasgow. It is a commercial centre in a mainly residential area of the city, home to approximately 8000 people. The A77 Pollokshaws Road (in red) goes from South West to North East at a 30mph speed limit, and two smaller roads of 20mph limits link onto this main road. These tributary roads are Moss-Side Road (in orange) and Kilmarnock Road (in green). All roads linking into the junction are 2 lane dual direction roads, permitting regular traffic such as standard cars, lorries, buses and cyclists. All roads have car parking bays on both sides of the road, which appear to be taking up a car width portion of the road. In the same lanes, bus stops indicate a high level of public transport usage in the area.

The roads are relatively flat, with no noticeable steep gradients or hills which could affect traffic in wintery conditions. Gradients are shown in figure 2, taken from heights above sea level from digimap. In addition, the roads are of reasonable quality, with no large potholes present, although there is a clear loss of colour in the traffic markings at the cross, which could lead to problems in the future over the clarity of traffic instructions.

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Fig. 1

Fig. 2

Traffic is regulated using British standard traffic light systems and phasing, as shown in figure 1.

The traffic at the junction is mostly managed by traffic lights, but with Google Map analysis, police officers are also seen to be guiding traffic at nearby junctions, showing traffic management systems in the area are not adequate to allow the traffic to flow by automatic and computational means alone.

The road is primarily used to access the city centre of Glasgow, but is also used as a local hub for shops and facilities in the area, such as the Church and pubs near the junction. It can also be used as access to other towns in the area such as Newton Mearns and Rutherglen. It particularly grows in popularity during football games at the nearby Hampden Park National Stadium.

In addition to traffic movement, the area is commonly used for parking and drop offs for the nearby Shawlands Academy and Primary School with 1200 and 600 pupils respectively. This results in a large rise in congestion during school hours and in particular the morning and evening rush hours, as can be seen in figure 3 at 8.30am.

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Fig. 3

Fig. 4

Junction Operation

The operational degree of saturation (x) and delay time of the junction shall be calculated using the equations:

Where

qi= flow for each lane in pcu per hour. This is divided into 3 sections, the morning peak, the afternoon peak and the interpeak value between these two.

S=saturation flow in pcu/hour.

g= effective green time in seconds

C= also known as the cycle time in seconds

D=delay time in seconds

The AM peak values are displayed in the table below. The initial arrival flow was calculated into the pcu value from raw data taken from my place. This could allow the Q and X value to be calculated using the equation above.

The arrival flow in these data sets is the actual flow of PCU per hour during the given peak times measured. Q is the approach capacity, related to the saturation flow, and acts as the capacity in PCU per hour, showing the limit for capacity per hour, where if exceeded queues will begin to form.

X is the degree of saturation, which is found by dividing the arrival flow by Q.

Some cells in the data set below are combined due to sharing lanes. For example cars attempting to turn right onto Moss Side Road will share lanes with traffic going straight on to Pollokshaws Road.

The afternoon peak value was calculated using the same method with different raw data from My Place.

The interpeak time was calculated using the same method.

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x i=qi

Si( giC )

(Full data sets and calculations are available in the appendix section.)

The data shows the widespread nature of the congestion, where Moss Side Road shows very little sign of mass congestion. However, Shawlands Cross shows an extremely high level of congestion. A level of 1 for X shows a high level of congestion, with anything higher showing potentially significant queuing issues.

The delay times are similar for AM and PM figures, but lower during the IP time, suggesting the congestion is not a huge issue during this time, but must clearly be improved during rush hour times. The 2 minute wait drivers face coming from Shawlands Cross and attempting to turn right or go straight on to Pollokshaws during these times of day will likely cause frustration and potentially cause further issues.

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AMPM

IP

The flow is highest on Shawlands Cross and Kilmarnock Road at all times of day, this is due to these being the main roads leading through the cross and having a higher speed limit than the other roads in the cross. All of the roads in the cross appear to have high saturation values, meaning that there is likely to be high levels of congestion at all peak times. As can been seen in the table, traffic coming from Shawlands Cross and trying to turn right to Moss Side Road will face substantial delay. With this high saturation rate, high congestion is expected. The phasing should therefore be altered to reduce the saturation rate and therefore reduce congestion in the junction. For example, traffic coming from Moss Side is permitted a full 30 seconds to flow, despite having a rather low saturation flow. This time could be better spent in allowing traffic from Shawlands Cross to Pollokshaws or Moss Side Road, where saturation is considerably higher.

In addition, lane design could be altered to allow for a right hand turn only, and therefore reducing the flow in the lane waiting for cars to turn right when they are planning on going straight ahead to Pollokshaws Road.

Assumptions were made for the Shawlands to Pollokshaws section of road due to the road being an opposed flow. Simple equations are only available for an unopposed flow. For this, a literal approach was taken, where it was known that 8 cars were approaching per green light to the flow per green light cycle. This worked out as 3.25s per car, and considerations were taken for how many cars would attempt to cross during this brief break in traffic. It was estimated that 2 -4 may try, although this could be higher or lower depending on flow. Four cars were estimated to attempt to cross per green light as the actual flow. The saturation flow was calculated by working backwards using this estimated value.

From a non-motorist perspective, the junction would most likely seem impractical. There are no noticeable or consistent cycle lanes along the road, meaning cyclists must compete with motor vehicles for space along all roads, increasing the chance of accidents or problems between road users. Also, the main commercial sector of the town of Shawlands is along the road, and crossing the road seems problematic due to the awkward shape of the junction. In order to cross the road at sections, pedestrians must cross 3 sets of pedestrian crossing. The new design for the junction could incorporate all of these concerns to make the junction a safer and more efficient area for all those who use it. The pedestrian walkways seem to be of a reasonable quality in terms of footpath quality, although the paths appear to have been affected by winter freeze thaw weathering like the roads, with minor potholes in places.

To summarise the problems in Shawlands Junction, there is a distinct inefficiency in the phasing of the traffic lights, where cars are given unsuitable time for passing through. In addition to motor vehicle use, the facilities are not in place for a safe and efficient usage from cyclists or other non-motorised users of the road. In order for this to be improved, designated lanes must be added for cyclists, and possibly buses if there is room for this on the road. The pedestrian users of the junction must be considered for the changes in the junction. Currently it is highly inconvenient for crossing due to the layout and position of crossing points, in particular the North to South crossing of the A77. This results in a high potential for accidents. Improvements in all of the above issues will result in an increase in safety, efficiency in the junction in terms of congestion, and also improve the economic benefit to the nearby commercial area along the cross.

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There is however a potential for improving this junction significantly. If the data from traffic counts for each section of road can be studied, then a more efficient phasing plan can be suggested, resulting in a lowering of congestion. This will mean greater efficiency and safety for all those who use the road. There is potential for the road to be widened, allowing for facilities such as a cycle lane or bus lane to be added, this would lead to further safety. In addition, right hand turns only could be accommodated for in order to reduce the overall flow per lane, and therefore reduce waiting times and congestion. This would of course have to compromise the pedestrian footpath, but if this could be redesigned for better crossing point then it is possible such a wide path would not be required. This would be down to more efficiently guiding pedestrians to their destination rather than requiring footpaths in places pedestrians could easily find a more efficient route.

This would reduce the need for the high number of railings in place, which attempt to guide the pedestrians the long way round to the inconvenient crossing points, as seen in figure 5.

The current crossing positions are marked on figure 6 as red lines, with possible new positions marked in blue. If this was followed, then pedestrians would have less distance to walk, and pavements could be narrowed to implement cycle lanes. This could be operated as once large scale pedestrian crossing point, where all traffic must wait for the pedestrians rather than particular roads stopping for particular crossings.

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Fig.5

Appendix

Raw Data

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Junction Observation Full Table and Calculation

Sources

http://digimap.edina.ac.uk/digimap/home

Google Maps

Myplace.com

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Lane Width Turn Radius Gradient So3 0 -0.015514978 20553 0 0.007578947 2054.6823 0.007578947 2054.682

3 0 -0.015514978 2055

3 0 -0.0035 20553 -0.0035 2055

3 0.019196928 2054.194


3 0 -0.015514978 2055

3 0 -0.0035 20553 -0.0035 2055

3 0.019196928 2054.194


3 0 -0.015514978 2055

3 0 -0.0035 20553 -0.0035 2055

3 0.019196928 2054.194

3

-

- - -

12 0.019196928 2054.194

- - -

12 0.019196928 2054.194

-

3

-

3

- -

12 0.019196928

-

2054.194

http://digimap.edina.ac.uk/digimap/home

CL318 Class Notes

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street design final submission

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