HIGH-SPEED ROADS
D3.7.25 The application of temporary mandatory speed limits should be considered for all planned works on high-speed roads, i.e. roads with a permanent speed limit of 50 mph or more. Temporary mandatory speed limits are established for each site and made by means of a temporary traffic regulation order; see Section D3.39. Better compliance can be obtained with these than with advisory speed limits because they are more readily understood by drivers and they are enforceable.
D3.7.26 Table 3.5 shows recommendations for the appropriate speed reduction to limit the risks associated with specific traffic management features on high-speed roads. Usually these features are not concurrent, but in such situations the designer would need to weigh the assessed risks to determine whether it is appropriate to apply a greater speed reduction.
| Temporary traffic management feature | Speed reduction | |
|---|---|---|
| Restricted visibility(1) | restricted driver forward visibility | 20mph |
| Loss of hard shoulder | used as running lane | 20 mph |
| closure of hard shoulder refuge | zero | |
| Loss of vehicle restraint barrier(2) | without protection | 20 mph |
| with protection | zero | |
| Lane restrictions(3) giving rise to lane changing | other than light traffic flow(4) | 20 mph |
| light traffic flow(4) | zero | |
| Lane merge | other than light traffic flow(4) | 20 mph |
| light traffic flow(4) | zero | |
| Narrow lane width(5) | HGV lanes less than 3.3 m and other traffic lanes subject to width restrictions less than 3.0 m | 20 mph |
| Contra-flow traffic management | with or without narrow lanes | 20 mph |
| Crossovers and changeovers | determined by design speed | see TA 92 "Crossover and changeover design" (DMRB 8.4.6) |
NOTES:
- For example, where a works structure or road works feature is likely to obstruct a driver's forward visibility and the sight line distance is likely to be reduced below the desirable minimum.
- The speed reduction where there is loss of vehicle restraint barrier should be related to the risk. Reference should be made to TD 19 "Requirement for road restraint systems" (DMRB 2.2.8) and the risk assessment tool. Where a vehicle restraint barrier is removed from the central reservation as part of the temporary works and a temporary barrier, or an Impact Protection Vehicle (see Part 2: Operations, Section O5) equivalent, is not installed, or is installed but does not provide an equivalent containment level, it should be classed as without protection.
- Where lane restrictions apply, e.g. lane closure, weight, width or height restrictions.
- Refer to the Glossary (Appendix 2) for the definition of light traffic flow.
- Lanes less than 3.3m wide that are required to carry HGVs, including public service vehicles, or lanes less than 3.0 m wide which are subject to vehicle width restrictions, are to be considered as narrow lanes.
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