Earlier this year. Speeding along the motorway, you cruise up behind a dark green people carrier and, as you overtake, glance at it casually. Bizarre! No bored, quarrelling children or excited dogs in this multi purpose vehicle.
The dark green space machine has been stripped of its middle seats and, with the addition of a paper-strewn desk, turned into a high-velocity office. In it sit a pair of men, their faces rigid with concentration and drawn with fatigue. The driver has the long distance stare of professional. His companion, at the rear of the vehicle and out of speaking range, is hunched intently over a laptop computer. They look purposeful, sinister.
The passenger jabs his computer and you can see the driver notching you up on a mental score sheet. They appear to be counting.
And, in fact, they are, or rather, were. The green MPV - colour deliberately discreet - was one of three identical units deployed by consultant Thorburn Colquhoun between autumn 1998 and spring this year to collect data for the National Speed Survey. Its crew, measuring average traffic speeds on the trunk roads and motorways of England, were obliged to carefully register the number of cars that passed them and diligently overtake an equal number of slower vehicles.
Thorburn Colquhoun carried out the £100,000 NSS for the Department for Environment Transport and the Regions. Technical director and survey project manager Jon Forni details the exacting task.
England's spaghetti of roads was chopped up into carefully measured sections with reference to the Network Information System, which charts routes and junctions designated significant by the Highways Agency.
The crews had to run a preselected length at a precise time of day. En route, they were required to log times through every segment as well. It was a job which required focus and anticipation - one glitch or slip- up and the section had to be redriven.
Equipment for the survey was relatively straightforward, says Forni. The MPV's speedo was wired to a laptop computer running Ariel II (Advanced Road Information Event Logger) software designed by Thorburn Colquhoun, which records distance at two-second intervals.
Distance and time data were located in relation to specific bits of road with the aid of a second piece of software, Mapinfo. This contained detailed run descriptions, including section numbers. The millions of lines of speed information generated were then delivered to the Agency for analysis.
The NSS is a monument to the average. It was conducted in a pair of two-month chunks - spring and autumn were favoured because day and night are of roughly equal length and there are no major holidays to distort humdrum normality on the roads.
Each section of road was driven at different times of year, and in each season it was also run at peak and off-peak times. To iron out anomalies runs were replicated on different days of the week. The total distance travelled was 65,000 miles, says Forni. Journeys to and
from the survey sites were extra, he adds.
Four months in a van takes its toll on a man. 'Compatible personalities are very important,' Forni understates. A penchant for Whitbread Travel Inns is handy too. Thorburn Colquhoun had to reconfigure a couple of teams to head off possible road rage. Even so, 'one of the reasons the car was so big was that it helped keep stress levels down'.
Thorburn Colquhoun transport planning associate director Mike Horsfall, out on the road with a driver called George, recalls: 'One night it was howling down with rain.' At the end of their run Horsfall navigated them off the trunk road. 'We ended up in no time in a country lane. The more we tried to get back on course the more and more hopelessly lost we became. By the time we found our way George wasn't talking to me.'
But they were united in agreement that 'the one way system in Cheltenham is nightmarish. We ended up in a garage buying a local map.'
On the road the crews thought that traffic speeds had come down compared to 1995 when the last survey was conducted. Nonetheless, 85mph was a fairly normal pace for drivers belting up the country's motorways. England's fastest motorists, they confirmed, drive red cars.
And Suffolk and Norfolk, where the black-top is straight and flat, harbour the highest proportion of speed freaks.