Coton Road Traffic

Tackling speeding on Coton Road, Grantchester

Please note, this article was published before a consultation last year. The consultation showed general support for the proposed signs, with a view that the location of the proposed sign near Bridleway be moved towards Stulpfield Road to near the old telephone box. An updated article will follow soon.

Speeding traffic on Coton Road is causing much annoyance amongst those living on the road. This is due both to the noise disturbance and to the serious safety concerns for young children and those with driveways adjoining the road, especially at the North-Western end of the village near the edge of the speed restriction.

The 2004 Parish Plan documented the desire amongst village residents that tackling speeding on Coton Road should be a priority for the village.

Subsequent meetings of Coton Road residents called for physical traffic calming measures. The preferred option was a series of speed humps of a type known as a "speed cushion". The proposal was adopted and pursued by the Parish Council. A basic speed survey was conducted for us by the County Council (measuring speeds between Bridleway and Stulpfield Road) and funding was investigated. The idea was eventually abandoned on cost grounds when funding could not be secured. A cheaper alternative of vehicle activated signs (see below) is now being considered by the Parish Council.

Speed Survey

The parish council commissioned a private speed survey in February 2008. This was carried out from Saturday 23rd to Friday 29th February, near the bus stop midway between the farm buildings and the Anglia Water pumping station (refer to map, although the location is not specifically marked).

The survey was carried out by Mouchel, and provided detailed data on numbers of vehicles, direction and speed, broken down by hour of the day throughout the week.

We have analysed the data that Mouchel provided and have presented it graphically in the following documents:

• Number of vehicles per hour in each direction.

On weekdays the morning peak is between 7am and 10am, reaching a maximum between 8am and 9am. This morning peak is seen only for vehicles entering the village. There was no morning peak in the other direction.

The weekday afternoon peak is only seen for vehicles leaving the village (between 5pm and 6pm) and is significantly less than the peak in the other direction in the mornings.

The volume of traffic at the weekends is similar to that during the middle of the day during the week, with an increase in vehicles leaving the village late afternoon on the Sunday.


• Graphical representation of vehicle speeds and number of vehicles per hour at each speed range, by time of day.

Speeds are grouped into "buckets" of 5mph each. For each hour the charts show a bubble per bucket, with the size of the bubble indicating the number of vehicles that were recorded as travelling at a speed in that range. The 30mph speed limit is indicated on each chart by a red line.

The relative amount and density of the blue colour above this red line approximately illustrates the relative number of vehicles exceeding the speed limit. Small bubbles indicate speeds of a small number of vehicles; large bubbles indicate frequently observed speeds.

There is a separate chart for each direction for each of Saturday, Sunday and the weekdays combined. As the vehicle-counts in the first document illustrate, all of the weekdays are approximately the same and so are not shown separately.

The tidal flow consistent with commuting through the village towards Cambridge in the morning and away in the evenings is evident in the weekday charts. Notice that the vast majority of vehicles are clearly substantially exceeding the speed limit, with several more than doubling the legal limit, travelling in excess of 60mph. Almost every vehicle late in the evening and early morning was travelling in excess of 30mph.


• Percentiles of one-hour speed distributions by time.

The percentiles charts show the minimum speed below which various proportions of the vehicles were travelling, for each hour of the week. For example, the line for the 95th percentile shows the speed below which 95% of all vehicles were travelling in a particular hour, and conversely this is the speed exceeded by the remaining 5% of the vehicles.

Where there is no line drawn, there were insufficient measurements during that hour to calculate the percentiles of the distribution and as such no conclusion should be drawn. Instead refer to the bubble charts in the second document for an indication of speeds during those times.

The first two charts show each direction separately. The final chart overlays some of the percentiles for each direction: the lighter lines show the percentile speeds of vehicles leaving the village. It can be seen that the speed of vehicles leaving the village tends to be higher in any particular hour than the speed of those vehicles entering the village during the same hour.

Vehicle Activated Signs

The Parish Plan consultation showed that the majority of people in the village believe that vehicle-activated 30mph signs should be installed at the entrance to the village on Coton Road. Provision has been made in the Parish Council's 2008/09 budget to directly fund such a sign, possibly one for each direction.

The Parish Council proposes the installation of two electronic vehicle activated signs on Coton Road. These would be triggered when a vehicle approaches in excess of the speed limit.

The signs that we propose to install will normally appear as a plain matt-black square on a post. They will light up only if a vehicle approaches too quickly. When activated, the sign will repeatedly switch between showing a 30 speed limit symbol in a red circle, followed by the words "SLOW DOWN". Shortly after the speeding vehicle passes, the sign switches off again.

The type of sign that we propose to install is shown here:

• 30mph roundel (60cm) / "SLOW DOWN"

Whilst it is understood that these will not influence the behaviour of every driver, the aim is to encourage a significant proportion of drivers to reduce their speed to safer levels. Research shows that 85% of people hit by a vehicle at 40mph will die, compared with 20% at 30mph and 5% at 20mph.

Proposed Locations

We propose to install two signs. One facing westbound traffic, just before Bridleway; the other opposite 75 Coton Road, facing traffic entering the village.

Mock-ups of what the sign might look like in the proposed locations are shown below.

 Proposed westbound sign - view from near Stulpfield Road

 Proposed westbound sign near Bridleway - closeup

 Proposed eastbound sign - view from village sign

 Proposed eastbound sign opposite 75 Coton Road - closeup

These locations were carefully chosen in an attempt to balance a number of factors. Some of these are as follows.

For the inbound sign:

• Vehicles must already be within the 30mph speed restriction when they activate the signs.
• The suggested location is visible for a reasonable distance immediately after vehicles enter the speed restriction, encouraging drivers to reduce speed as early as possible.

For the outbound sign:

• The location has a long approach, maximizing the distance over which the sign is likely to influence vehicle speeds.
• The location is not too close to Stulpfield Road or the start of Coton Road, where many vehicles may not yet have accelerated sufficiently to activate the sign, limiting its effectiveness.
• Drivers will have been reminded of the speed restriction as late as possible prior to the corner after Bridleway. A sign located after that corner would have only a short approach where it would be visible and would not have any influence on vehicles entering the blind corner.
• The suggested location is intended to minimise the visibility of the sign through windows of living spaces in nearby properties.

Consultation

There will be a public meeting at 8pm on Wednesday 15th October 2008 in the Reading Room. Please come along to find out more and to express your views on this proposal. The Parish Council will subsequently make a decision about how to proceed, taking into account all comments received either at the meeting or in writing.

If you cannot attend the meeting or would like to pass on your comments in writing, please send a note either by email to coton.road@grantchester.org.uk or drop a note to 67 Coton Road.