Please find below a rationale of the newly designed junction at Newell A30.
Dorset Council has had several enquiries from the public around certain aspects of the build. Highways Improvements have put together some further information, shown below, to help resolve any queries.
No Cornhill Signals
It is a long-held aspiration of the Town Council and Dorset Council councillors to reduce the volume of traffic using the A352 Westbury / Acreman Street / Cornhill corridor. A new layout of the junction of A352 Ottery Ln / Westbury is being considered to support this aim.
The Public Consultation drawing (HI1222_300_2_Orig) showed the proposals, including the removal of the traffic signals on the Cornhill approach. This was distributed to the primary stakeholders; no adverse comments were received about the proposals.
The A30 Kitt Hill stopline has been moved forwards approximately 17m. This improves the [signal] junction intervisibility, reduces the Phase-to-Phase intergreen times, reduces lost time, and reduces the number of Stages. This improves capacity, reduces congestion, and improves air quality. The cycle time is lower which allows pedestrian / cycle demands to be serviced more quickly.
The Puffin crossings have been replaced with Toucan crossings. The crossing of A30 Kitt Hill is approximately 12 metres further forwards, closer to the desire line and at a point where the footway / cycleway is wider. The crossing of A30 Newell is approximately 8m further forwards, closer to the desire line. The crossing of B3148 Marston Rd is in its original location.
Traffic coming from Left and Right when Giving Way (from Cornhill)
Extract of Public Consultation drawing (dated 14 Jun 2022)
Notes:
Stages – contain one or more Phases and are given numbers.
Phases – individual traffic (or pedestrian / cycle) movements are given letters.
Intergreen – the time between one Phase losing right of way and another Phase gaining right of way.
On a move from Stage 3 to Stage 1 Phase A starts as normal but Phase B is delayed by a short time. This generates gaps between the Keep Clear marking and the stopline on A30 Kitt Hall and gives traffic turning right from Cornhill a clearance period during which they can move forwards, with no traffic coming from their right.
The traffic signals now revert to All Red (Stage 5) in the absence of any demands. This reduces traffic speeds on all approaches, especially during quiet periods.
Visibility to left (A30 Kitt Hill)
Speed of traffic from left (A30 Kitt Hill)
We follow clear guidance from the Department for Transport when designing/altering the highway, this includes clear guidance on sightlines for drivers.
The 85% approach speed on A30 Kitt Hill is low enough to allow the visibility to the left to be calculated in accordance with Manual for Streets 2 (MfS 2).
The Give Way road marking, and the single dashed line, aligns Cornhill traffic at 90 degrees to A30 Kitt Hill. From this point, the visibility to the left complies with MfS 2.
The hatched area to the right can legally be driven into as it is not bordered by a solid white line. It is there to allow drivers flexibility to position their vehicles. From this point, the visibility to the left also complies with MfS 2.
Size of Keep Clear marking on A30 Kitt Hill
The Keep Clear marking is 6m long which is the generally accepted length of a queuing vehicle. The distance between the Keep Clear marking and the downstream stopline is sufficient for two queuing vehicles. The effective length of the Keep Clear marking is longer than 6m.
Drivers have been observed complying with the Keep Clear marking, and in some cases keeping the whole area between the first Keep Clear transverse line and the stopline clear if they see drivers waiting to turn right from Cornhill.
Overall, drivers using this junction have been observed doing so with due consideration to each other.
Bollard on island on Cornhill
This bollard highlights the presence of the island rather than giving direction instructions to road users. The options for the legends on that bollard are:
- Keep Left – this is inappropriate as it would compel all vehicles (cycles included) to pass to the left of the island.
- Keep Right – this is inappropriate as it would compel all vehicles to pass to the right of the island.
- Pass either side – this is also inappropriate as it would permit drivers to pass to the right of the island to reach the same destination.
Cyclists can access the new shared-use footway / cycleway via the short link on Cornhill by passing to the right of the island and giving way to any traffic turning left into Cornhill.
The speed of this traffic has been reduced by the widening of the footway / cycleway, the reduced radius of the corner and by the addition of dashed white lines across the entrance to Cornhill.