As part of the 20mph speed limit project, the City Council have collected a lot of data about current traffic speeds in north Cambridge, where the first phase of the project is due to be rolled out. Commendably, they have made this data available to anyone who wants it. There is an enormous amount of it – over 200Mb – giving a very detailed picture of traffic speeds in this part of the city. Here’s a first look at some of it.
There are broadly three categories of roads in the north area, shown on the consultation map [2.8Mb PDF] as green, blue, and dotted red. The green roads are A and B roads that will remain at 30mph; the blue roads, where most of the traffic is going to or from peoples houses – these typically already have slower traffic speeds. The dotted red roads are probably the most controversial – they have faster traffic, much of which isn’t immediately local residents, but they are being considered for 20mph limits. The maps [6.3Mb PDF] from the public exhibition posters show the current traffic speeds on all the roads – speeds were measured at each of these locations from 5th to 18th March. You may remember seeing the measuring devices around the north of the city. They can apparently record the type of each vehicle that passes as well as its speed.
Here are some graphs from some of the measuring points, showing the speeds of traffic (excluding cycles). First, Gilbert Road:
Almost all the traffic is going faster than 20mph, with nearly half the traffic travelling between 25 and 30mph. Of course traffic speeds vary with time of day and day of the week – the graph above gives a summary of the whole period that speeds were measured for. This graph shows the speeds measured between 8am and 9am (though this includes weekends as well as weekdays):
As you can see the speeds are noticeably slower, but still with the great majority of the traffic at over 20mph. In contrast, here is the graph for Akeman Street, a largely residential street with a row of shops in the same part of town, which has speed bumps:
Here the traffic is much slower, with most of it below 20mph.
One of the red dotted roads is Arbury Road, which had three separate speed measuring points. Here are the southbound speeds for the middle one, showing most traffic over 20mph:
Another red dotted road, Green End Road, is a good deal slower, with most traffic only a little faster than 20mph:
Finally, here is the fastest of the red dotted roads, Kings Hedges Road. Unfortunately it seems to have had only one measuring point, towards the Milton Road end:
Nearly half the traffic recorded was exceeding the existing speed limit of 30mph.
The City Council’s consultation is continuing until 5 July, and I’ll be writing more about the project in future posts.