Trumpington Street roundabouts

diagram

What is proposed?

The county council is proposing some temporary changes to the double roundabouts at Trumpington Street/Road, Lensfield Road and Fen Causeway. These changes include lane reductions to improve road safety and widening of pedestrian refuge islands.

Our thoughts and position

The double mini-roundabouts at Trumpington Street/Road, Lensfield Road and Fen Causeway have consistently been rated one of the top-5 most dangerous places in the county for decades. It’s a lethal combination of excessive lanes for motor traffic leading into jammed mini-roundabouts and near-zero provision for pedestrians. Therefore we are glad to see that the county is trying to consider some steps to alleviate the danger here. However, while things are moving in the right direction, it really doesn’t go far enough.

Starting with the positives:

  • Some lane reductions on Trumpington Street and Trumpington Road approaches to the mini-roundabouts.
  • Lane reduction on Lensfield Road from two to one provides space for a decently sized pedestrian refuge in the centre of the road instead of the tiny and pitiful existing refuge.
  • Carriageway reduction on the road between the two mini-roundabouts brings the total number of lanes from four down to two, thus slowing motor traffic and increasing pavement space.

And the negatives:

  • There are still too many lanes approaching the mini-roundabouts from Trumpington Street, Trumpington Road and Fen Causeway, which means insufficient deflection and speed-reduction.
    • For safety’s sake, all of the roundabout entries and exits should be single lane. This greatly simplifies navigation of the roundabouts, for all road users.
  • Lack of deflection means that drivers are more likely to shoot across the roundabout without looking for cyclists or pedestrians first.
    • This is a ubiquitous problem with mini-roundabouts, which is why in general we advise against their installation. Roundabouts function best when there is a physical central island and all of the carriageways are kept to the absolute minimum possible width they may be, in order to force the deflection of motor vehicle paths and therefore keep speeds as low as reasonably possible. Low speeds are the secret to both safety and capacity and such roundabouts function better for all road users.
  • The pedestrian crossings of Trumpington Street and Lensfield Road are somewhat improved but still rather difficult to use because of the multiple lanes and rather close proximity to the mini-roundabout.
  • No crossing is provided of Fen Causeway apart from a Zebra crossing that is far away from the desire line.

Does the proposal meet DfT guidelines?

Yes, the scheme is proposing road space reallocation in favour of walking and cycling. However, we believe it could be significantly improved.

What would we like to see?

At a first approximation, the following changes could be made to the scheme without resorting to traffic signals:

  • All the roads and junction entries and exits should have no more than a single carriageway lane in either direction.
  • The mini-roundabouts could be replaced by priority junctions. This could be either with straight-up T-junctions, which would be simplest, or with bent-priority junctions arranged to prioritise the ring road traffic.
  • The reclaimed carriageway space could be used for cycle lanes with lightweight segregation. In front of the shops on Trumpington Street there could also be additional cycle parking and marked delivery bays.
  • The scheme should be extended south in order to connect with the Trumpington Road outbound cycle lanes and to build the long-belated inbound cycle lanes that were consulted on years ago and then put aside. This would add more cost; however, these lanes were already intended to be installed years ago but unfortunately have been delayed.

Ultimately, this junction should return to being under signalised control, however that will take a lot more money and time to design and build. In general, long-term traffic reduction measures for the city centre would also have a great benefit here, as the fundamental problem is too many cars.