Page:UK Traffic Signs Manual - Chapter 8 - Part 1 (Traffic Safety Measures and Signs for Road). Designs 2009.pdf/29

DESIGN CRITERIA the imposition of a temporary mandatory 10 mph speed limit. For both single and all-purpose dual carriageway high-speed roads, a temporary maximum speed limit of at least 20 mph lower than the permanent limit should be imposed in advance of the 10 mph limit.

Where on bridges, other structures and in tunnels, the overall width of highway is limited, making it difficult to maintain an adequate traffic capacity with the full lateral clearance, a reduced safety clearance may be considered in conjunction with the enforcement of a reduced mandatory maximum speed limit of 40 mph or less, see paragraph D3.2.12.

Direct risks to the safety of the workforce should be countered by the presence of vehicle restraint barriers or changes in working methods that eliminate the risks. Temporary speed limits should not be imposed at road works sites solely for the direct purpose of protecting the workforce. The presence of vulnerable work operations on foot should be minimised. When direct measures to ameliorate identified risks to workers are not likely to be fully effective at the permanent speed limit, or represent an increased risk to road users, the imposition of a temporary speed reduction should be considered.

Under normal circumstances, temporary speed limits should only be imposed at road works in response to temporary hazards arising from the temporary traffic management arrangements. However, when road works involve a number of discrete works areas which are within 800 m of each other, it may be appropriate to continue the temporary speed limit between sites irrespective of the presence of temporary traffic management arrangements between sites.

Where changes to the work being undertaken remove or alter the need for temporary traffic management, the extent of any temporary speed limit should be adjusted to match the new temporary arrangements. A temporary speed restriction shall not be left in force once works are completed (or where works are left in a part complete state for any significant length of time) unless its immediate removal would pose additional risk to road users. It is not acceptable to maintain traffic management to justify the retention of a temporary speed limit or to maintain a temporary mandatory speed limit where there is no overall risk benefit in so doing.

Where works are suspended or part suspended during holiday periods, temporary speed limits should also be removed unless any remaining temporary traffic management required to protect part complete works also presents a risk to road users. In situations where lane closures are reduced to hard shoulder closures, it would be expected that temporary speed limits would be removed or set at a higher level.

Where it is anticipated that regular imposing/removing of speed restrictions will be necessary, consideration should be given to using remotely operated signs for safety reasons.

Traffic regulation orders should be written in a form that will allow temporary speeds limits to be changed to reflect alterations in temporary traffic management over the length of the works. If the temporary speed limit is required for purposes other than in support of temporary traffic management arrangements it is essential to ensure that the temporary speed limit order is still applicable or another order is promoted to address the particular reason (e.g. solely safety related) for the speed limit remaining.

Temporary speed limits should generally be imposed 50 m in advance of the first sign at road works indicating a restriction or lane closure, On a two-lane single carriageway road this is likely to be the "road narrows ahead" sign to diagram 517 and on a dual carriageway road a lane closure sign to diagram 7202. This ensures that speed restrictions apply to the sector of the temporary traffic management arrangement in which vehicle manoeuvres or lane changing tends to occur.

Speed restrictions should extend to a point, 90 m for dual carriageway roads and 45 m for one-way single carriageway roads, beyond the last cone of the temporary traffic management arrangement. However, on two-way single carriageway roads, to ensure that the speed limit is enforceable, the signs indicating the end of the speed restriction must be located back to back with those in the other direction that indicate the start 28