Sunday, 28 October 2012

Vehicles per hour on the Cambridge commute

Way back in March 2011, the Police did one week automated speed surveys in Cottenham. Here are a few facts and figures with a focus for cycle commuters going to and from Cambridge. Cottenham is 7 miles north of central Cambridge.

The numbers are only for the peak hours Mon-Fri. Vehicles per hour are in one direction. Traffic levels drop off significantly outside of these hours. Averages are median of 5 days totals.

Histon Road 30mph, Southbound towards Cambridge:
08:00-08:59  762 vehicles per hour, one car every 4.7 seconds. 24% >35mph.
09:00-9:59   790 vehicles per hour, one car every 4.6 seconds. 15% >35mph.
The amount of traffic arriving at Twenty Pence Road on the northern edge of Cottenham is 74% and 76% of the Histon Road levels.

Histon Road 30mph, Northbound returning from Cambridge.
16:00-16:59  378 vehicles per hour, one car every 9.5 seconds. 24% >35mph.
17:00-17:59  566 vehicles per hour, one car every 6.4 seconds. 21% >35mph.
18:00-18:59  695 vehicles per hour, ne car every 5.2 seconds. 18% >35mph.
The amount of traffic exiting at Twenty Pence Road is 56%, 60% and 57% of the Histon Road levels.

Before 9am has always had an more edgy and rushed feel to it - my instincts are right. My instincts also tell me that 8:50am is a terrible time for speeding, worse than 8:30am and I have wondered if this is the gonna-be-late-for-work effect.

I have also noticed that traffic in the 4pm slot is running faster and I have suspected the white van effect. A quick scan of the raw data suggests that Category2 vehicles (>6m long) are only 10% of the traffic on Histon Road and do not speed more than other vehicles.  Exiting on Twenty Pence Road however, is a very different story, with a much larger proportion of vans and 10% higher speeds than category 1.

I've included the numbers comparisons for Twenty Pence Road as I sometimes wonder how much traffic is passing through the village as an alternative to using the parallel A10 trunk road.  The A10 typically queues from just south of Waterbeach to the A14 roundabout and the B1049 offers a parallel route. It is interesting to note the lower percentages of traffic passing in the reverse direction in the evening which gives a little weight to my theory.

The section of Histon Road between the mini roundabout and the beginning of the cyclepath is exactly 1km. This equates to 2-4 minutes of cycling (10-20mph range).  Assuming a rate of one car every 5 seconds, you are going to be overtaken by 24-48 cars on this stretch.  With typically a fifth of cars speeding at 36mph or more, you can begin to imagine how many unpleasant overtakes a cycle commuter must endure if they cycle on the road. It's not just the speeding cars, there are a lot of drivers simply wanting to overtake and may get frustrated by a slower cycle and oncoming traffic preventing an overtake if you ride away from the kerb. Kerb huggers will have many of these vehicles squeezing through.

You can halve the number of unpleasant overtakes by cycling at a lycra roadie speed of 20mph.  If you can't, that footpath must look like a safe haven, a necessity even.


I thought I might as well record how many cars pass me on this 1km stretch to see how it compares to the Police recordings.  I normally spend 2.5 minutes on Histon Road.


October half term school holiday week (i.e. very quiet)

Southbound Mon 08:50am. Just 6 passes in 2.5 minutes.
Southbound Tues 09:20am. 7 passes. Feels like a Ghost Town compared to normal.
Northbound Mon 18:30pm. An unbelievable 5, yes just 5.

November, during school term:
Southbound Wed 8:50am. 12 passes. (plus queue after I pulled onto path)
Southbound Thu 9:00am. 11 passes + 7 queued behind.
Southbound Fri 9:00am. 6 passes.
Southbound Mon 9:30am. 12 passes. (very little oncoming traffic, overtaking easy)
Southbound Wed 8:55am. 8 passes.
Southbound Thur 9:05am. 9 passes.

Northbound Wed 6:50pm. 6 passes (had to wait for traffic to clear)
Northbound Fri 6:00pm. 0 passes (very unusual!)
Northbound Wed 7:00pm. 4 passes.
Northbound Thurs 7:30pm. lost count, was distracted by overtakes at high speed.

I give up!  I lost count too many times when distracted by overtaking cars rushing to overtake in gaps that were too small. I'd end up concentrating on staying alive rather than being relaxed enough to count.


  • Southbound, when a normal busy week there is enough oncoming traffic to prevent cars overtaking if you ride out from the kerb. If you ride in the gutter the queuing cars will squeeze through.
  • Lack of overtaking opportunities because of oncoming traffic leads to frustrated drivers sitting on your tail right where you can't see them and where you feel most vulnerable.
  • Northbound, at the end of the cyclepath there is often a wave of traffic that has been released by the traffic lights in Histon.  Sometimes have to wait for the traffic to clear, sometimes it is clear then you get engulfed whilst on the road.


  1. Is it possible, for a non local, to give an idea of how big/wide/the lighting is on this road. I often use a wide 30mph road where such speeding would not be an issue - but there are other roads locally, where such speeding would result in "concern"?

  2. Hi Mike, it's Histon Road, Cottenham. See on Google Streetview. It is built up, and lit by street lights. The traffic levels are intimidating to most, and a cyclist on the road will cause a few cars to wait for an overtake or if you hug the gutter squeeze between you and oncoming traffic.

    It is a 30mph road, probably quite typical of village through roads near to large towns and cities, exactly the sort of road that attracts low cycling rates and brave male riders aged 30-50.

    What's different here is that the council are trying to improve cycling rates for those travelling into Cambridge as part of a strategy to keep traffic levels in check. A great deal of money has been spent making a cycle path to attract more cyclists, and as a result we are seeing an increase in all cyclists, not just male but also females and teenagers. The cyclepath starts at the edge of the village and start of a 50mph zone. The 30mph section with rush hour levels of traffic is still intimidating to most and mostly females and teenagers can be seen riding the footpath illegally, but quite understandably for their own safety.

    Brave males do cycle Histon Road without making a huge fuss.

    1. hmm - see what you mean - its rather narrow - I'm in the "brave cyclist, 49, age group"

      Is there an attitude problem - here in "Greater Bristol, it seems there is a lot of patience from drivers - obviously not all and not all the time, but even though Bristol has suffered from 60's planning blight, there is somewhere near a critical mass of cyclists and some ok infrastructure.

      Its not universal. There are places which are less happy - and I guess we are lucky with a lot of cycle paths following the ring road, the Bristol-Bath cycle way etc. There is also the "marginalisation" of 4 wheels with bus lanes open for cyclists and motorcyclists (I am one too)

  3. Hi, it seems like you use this route alot, have you asked the Council for the safety audits under the FOI of the cyclepath crossing when coming from Histon back into Cottenham? Especially now that the clocks have changed and the route is in the dark. ;)

    Can you give me a time and place to meet sometime so that we can chat?

  4. Safety audit! After the on road lanes went in near Histon Green I was waiting for the safety audit. After a while it was revealed to me that the safety audit is for car traffic only! A massive culture change is required not just in our council, but in all councils across the country. I guess you've been reading about London safety audits, I am surprised they even consider cyclists but things are changing for the better in London and will hopefully spread to other areas.

    Regarding the crossing of the road at the end of the cyclepath. It was originally specified with a traffic light crossing but that was cut due to money. Cutting a long story short, to build a complete and adequate cycle network, requires central government money.

    There is support for action on Histon Road, our voices have been heard by the local councillors so there is no need to bust through an open door. There has been talk of a speed reducing entry feature and the Dec 2012 issue of Cottenham News, Parish Council section says they are in discussion with the County Council re speed reducing measures of Histon Road. Keep an eye on councillors minutes for updates.

    Ultimately, I think there is too much motor vehicle traffic during the peak of the rush hour and cyclists and cars need to be segregated. For me, the worst place on Histon Road is the corner at Cossington Close, with risky overtakes but speeds already near 30mph; followed by the crossing point at the edge of Cottenham.

    If you want to talk about anything else face to face, send me a direct mail on Twitter.

  5. Hi, I hope you agree we are all after the same cause, a safe and useful cycleway and footpath.

    The Council have a responsibility to undertake Safety Audits and have conducted 3 so far. They also need to do an Audit now that the clocks have changed. This needs to be done in the dark to raise any issues with crossing the road in the winter / dark.

    Previsous Audits - and nothing has been done about the crossing -

    22 September 2009 -

    A1.1 Problem

    Location: North end uncontrolled crossing.

    Summary: Possible high speed approach as peds/cyclists cross.
    Although the visibility is good in this location the pedestrians and cyclists may have difficulty in determining the approach speeds due to the close proximity to the change in speed limit. Drivers from one direction should be slowing to the reduced limit whilst those from the other may be speeding up. This could result in poor decision making and collisions between cyclists and vehicles.


    Ideally relocate this crossing point further into the Village where speeds should be slower.

  6. 14th March 2011 -

    The accidents have been assessed between Jan 05 and Jan 11.
    There have been a total of 15 injury accidents of which 2 were fatal, 2 were serious and 11 were slight.

    • An un-ridden horse collided with a vehicle.
    • U-turning in a driveway the vehicle collided with another vehicle.
    • Shunt type accident as a vehicle went to turn right.
    • A shunt type accident occurred as a vehicle turned right out of a junction.
    • 2 Single vehicle lost control at speed.
    • Child cyclist pulled out and collided with a vehicle on the main road.
    • Vehicle overtaking, swerved and lost control.
    • Motorcyclist clipped the kerb and lost control.
    • Cycle/vehicle collision.
    • Vehicle overtaking a cyclist collision occurred.
    • A shunt type accident.
    • 2 horses spooked and collided with vehicles.
    • Vehicle overtaking a cyclist collides with oncoming traffic.
    • Motorcyclist overtook a slow moving vehicle when back in lane lost control.


    Location: CH 1125.

    Summary: joining/exiting the shared use facility
    At CH 1125 it is not clear how cyclists will return to the carriageway or join the shared use facility. Cyclists may even stay off road and cycle along the narrow footway.
    This may bring them into conflict with pedestrians or other road users as they return to the carriageway.
    File Ref: G526 / Safety Audits/1404


    Ensure that the facility is either extended through to a safe location or entry/exit facilities are designed and included as part of this phase.

    B1.2 Problem

    Location: shared use path widths across the scheme.

    Summary: a narrow shared use facility may result in conflict between cyclists and pedestrians.
    From the drawing the shared use will be 2m wide at the narrowest point. However with 0.5m segregation strip and a 0.25m edge strip this only leaves a 1.25m wide shared use facility. Whilst this appears to be the case in some of the existing areas it may bring cyclists and pedestrians into conflict on the new facility.


    Ideally provide a wider shared use facility to avoid conflicts.

  7. Still no Action (these audits are only from the last house in Histon to Cottenham Green, they should have carried out more audits for Histon) - Interesting reading isn't it and nothing has been done.

    15 June 2012 -

    Problem B1.1

    Location: CH1125

    Summary: joining/exiting the shared use facility

    At CH1125 it is not clear how cyclists will return to the carriageway or join the shared use facility. Cyclists may even stay off road and cycle along the narrow footway. This may bring them into conflict with pedestrians or other road users as they return to the carriageway.


    Ensure that the facility is either extended through to a safe location or entry/exit facilities are designed and included as part of this phase.

    Designer’s Response
    No response received

    It is fairly common for drivers entering a lower speed limit to still be travelling at a higher speed for a period of time after the terminal signs and therefore speeds may still be high for vehicles approaching from Histon. This may encourage cyclists to remain off carriageway until they reach a point where the speeds of approaching vehicles may more accurately be judged, potentially bringing them into conflict with other footway users.
    Ideally the facility should be extended into the village and measures installed to highlight the crossing point to all approaching road users. If this does not prove feasible, it would still be prudent to give advance warning to drivers that they are likely to encounter crossing cyclists.

  8. Wow, I had no idea these documents existed, thanks for sharing. I guess you had to FOI request these, such a shame these are not in the public domain by default.

    The safety audits do confirm my experiences and are actually quite sane. One thing they do not reveal clearly is that the volumes of traffic right up to the green are pretty hostile during rush hour. Reading between the lines it's like 30mph means it is acceptable to have no facilities to protect cyclists.

    There is more information on the Stages of a Safety Audit on the CambsCC website. The Accident Sites link also reveals something about the priority across the County.

    As you point out, there is a glaring omission, and that is where it says "Designer’s Response: No response received".

  9. Hello, I'm glad in helping.

    I agree about the obvious omission and find it amazing that nothing has been done to complete the project and make it comply to current standards.

    It is now therefore time to get this out in the open before more people are killed or injured.

    Now that some of the issues have been made public (the Council also need to undertake an Audit in the dark and in rush hour, this is compulsory) can you notify as many others you know (including cycling groups, friends etc) that use this route so something gets done and is safe for all to use. is the person involved, so how about firing off an e-mail ;)

    Take care and safe cycling.

    If you need to get full copies of the Audits from the Council, ask for FOI 2041.

    Talk soon.