Green Dragon cycle traffic

With the recent discussion over walking and cycling on Green Dragon bridge I thought I would take a look at the actual number of cycles on the bridge.  There is an automated cycle counter at the bottom of the bridge although there are no automatic counters for pedestrians.

The headline figures are that there are in excess of 1000 cycles a day are counted at the bridge in both directions and the peak flow is typically around 250 cycles per hour.  That is a lot of people that could be inconvenienced by any changes to the bridge, and a lot to be accommodated in a path of only 2.3m width.  We also see that Cambridge people cycle year round, not just in the Summer.

Please read the notes below about the counters and what is actually counted.  I would like to thank Cambridgeshire County Council’s Cycling Projects Team for providing the data.

Seasonal hourly flows

Here I plot the figures per season to see what seasonal variation there is.  Inbound means towards the city centre, outbound means towards Water Street.

Green Dragon hourly flow SpringGreen Dragon total flow SpringIn Spring we saw:

  • A peak of 350 per hour
  • 366 total in the morning peak
  • 1482 total a day

(average figures for weekdays)
Green Dragon hourly flow SummerGreen Dragon total flow SummerIn Summer we saw:

  • A peak of 300 per hour
  • 266 total in the morning peak
  • 952 total a day

Green Dragon hourly flow AutumnGreen Dragon total flow AutumnIn Autumn we saw:

  • A peak of 350 per hour
  • 392 in the morning peak
  • 1403 total a day

Green Dragon hourly flow WinterGreen Dragon total flow WinterIn Winter we saw:

  • A peak of 310 per hour
  • 302 in the peak
  • 1171 total a day

Totals table

Here is the total counts per two hour period in table form

Time period Total cycles
Spring Summer Autumn Winter
(18 Mar – 11 June 2012) (18 June  – 10 Sept 2012) (17 Sept – 10 Dec 2012) (17 Dec – 4 Mar 2013)
00:00–02:00 12 9 9 8
02:00–04:00 2 2 2 2
04:00–06:00 21 18 16 12
06:00–08:00 153 111 143 101
08:00–10:00 366 268 392 302
10:00–12:00 91 62 95 83
12:00–14:00 81 45 77 78
14:00–16:00 103 55 109 102
16:00–18:00 236 128 243 213
18:00–20:00 243 139 194 166
20:00–22:00 116 73 78 63
22:00–24:00 57 42 46 36
All day 1482 952 1403 1171

Year-round flow

If you thought that people only cycle in the summer, the following chart shows the daily total number of cycles per weekday (based on a 5-day average).
Green Dragon Inbound total by weekThere is a noticeably lower level during the summer, no surprise in a city with two universities and other colleges and schools.  You can also see a pronounced dip over the Christmas and New Year period.

It’s clear that people in Cambridge cycle all year, and over this year we had very mixed weather!

About the numbers

The grey box on the right is the solar-powered cycle counter at Cutter Ferry bridge that sends its data over the GSM network

The grey box on the right is the solar-powered cycle counter at Cutter Ferry bridge that sends its data over the GSM network.

There are a number of cycle counters on key routes around the city that count the number of bicycles passing them every fifteen minutes.  The Cycling Projects Team at Cambridgeshire County Council kindly provided the data for the counters at Green Dragon bridge.  There are two counters here, one on the route to Fen Ditton and one near the start of the ramp to Green Dragon bridge.

Due to the location of the counters and their sensors neither record the number of cycles actually crossing the bridge.  Some cyclists continuing along the river and not crossing the bridge get counted on both counters while those going to/from Fen Ditton and crossing the bridge also get counted on both.  Rather than trying to combine the figures from the two counters to come up with an uncertain estimate of cycles actually crossing the bridge I decided to use just the figures from the single counter.  The typical numbers on the path to Fen Ditton are about 10% of the number at the other counter.

The cycle counter has two channels and on the advice of the Cycling Projects Team I have had to infer the direction of travel from the data.

I have just under a year’s worth of data that I have grouped in to four quarters, the start and end dates of which are somewhat arbitrary.  I hoped to get some insight in to these questions: Are there any seasonal variations?  Do people in Cambridge only cycle in good weather?

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