Delay:
(a) The value of time at 2002 prices for the average vehicle, available from the DfT’s Transport Analysis Guidance (WEB TAG) module 3.5.6. Paragraph 1.2.30, is £11.28 per hour, http://www.dft.gov.uk/webtag/documents/expert/unit3.5.6.php#012. Inflating to 2008 using the RTPI adds 22% yielding £13.76 per hour. Hence the delay cost for as few as 1,000 vehicles/day delayed for one minute at a junction amounts to £83,700 per 365 day year. See Spread sheet, sheet 1
(b) The 2006 National Travel Survey provides 430 car driver trips per head per year, NTS table 3.4. If we assume 55 million people then the total car driver trips per year amounted to circa 23.65 billion. Applying the average time cost for all vehicles (£13.76) to that and setting delay to two minutes yields £10.85 billion at 2008 prices. Cars account for 80% of traffic flow. However the journey lengths of other classes of vehicle may be longer and greater proportion of those trips may be in rural areas. Consequently those other vehicles will be less affected by traffic management measures. Hence in this calculation the delay cost of £10.85 billion suffered by cars is set to 90% of the delay to all vehicles, providing a total for all vehicles of £11.93 bn, Spread sheet, sheet 1
Diversions: Adding 1 km to 1000 journeys per day, where the speed is 40 kph (25 mph), costs £189,000 per year. Adding 1 km at 40 kph to all vehicle trips would cost £13.5 bn annually. Since most journeys start or end in urban areas and since it is there that most diversions occur, 40 kph (25 mph) is reasonable
(c) The WEB TAG provides formulae that generate vehicle operating costs. We used those to obtain a market price for those costs. Adding the time cost generated 51.88 pence per vehiclekm at 2008 prices including tax, Spread sheet, sheet 2. Multiplying by 1000 vehicles/day and by the 365 days in the year yields £189,400 per km
(d)If, as above, we take the 430 car driver trips per head per year and multiply by the population, here set to 55 million, and by 51.88 pence per vehkm we obtain an annual cost of £12.3 billion. Adding ten percent for other vehicles yields £13.5 billion.
Speed: Reducing the speed of 1,000 cars per day from 25 to 20 mph over 5 miles would cost £234,000 per year. The same for all cars and vans on urban roads would be £12.0 bn. A 5 mph speed reduction on cars and vans on all roads would cost £16.5 bn annually.
(a) The WEB TAG value of time for cars at 2002 prices is £10.5 per hour. Inflating by the RTPI to 2008, 22%, yields £12.81. Hence the time cost of slowing 1,000 cars per day over 5 miles from 25 to 20 mph is £5 x [(1/20) – (1/25)] x 1000 x 365 = £234,000 per year.
(b) In the following table the Vehiclekm are for cars and vans. The source data is from the 2008 TSGB as detailed on the attached Spread sheet, sheet 1 The speeds are those suggested by that TSGB tables 7.10 and 7.11 except for urban other where 25 mph rather tan 30 mph has been used as the initial speed. The value of time used is as above.
Casualty savings: TRL reports 421 and 511 provide accident savings per mph of speed change. The calculations in Spread sheet, sheet 3 use values based on those reports. The savings have a cash value of only £3bn. The table below summarises.
Time cost of 5 mph speed reduction on cars and vans and 


Vehkm 
Speed 
Time loss 
Casualty saving 
Motorways 
87.3 
70 
0.76 
0.133 
Aroads 




Rural Duals 
32.3 
69 
0.29 
0.695 
Rural Singles 
98.5 
53 
1.54 

Urban Duals 
31.6 
40 
0.90 
0.687 
Urban Singles 
44.6 
30 
2.36 

Other roads 




Rural 
68.4 
40 
1.94 
0.460 
Urban 
109.5 
25 
8.70 
0.916 

Sub total Rural 
3.77 
1.155 


Sub total  Urban 
11.95 
1.604 



TOTAL 
16.48 
2.892 