Average Speed

Introduction

I’ve received a number of e-mails regarding the calculation of the average speed of a journey, ranging from the “you’re sad, working it out” to “how do you do that?” Some individuals have asked why our average speed on the trip to Bournemouth was just 50 mph when we were cruising at a much higher speed on the motorway.

It’s all in the numbers.

The Calculation

I’ve written a very simple spreadsheet, originally for the Palm, that allows me to compute the average speed of a journey, or for various legs of the journey, but I have converted it to Excel and you can download it here. The calculation itself is very simple (and there are several ways to do it). The simplest to calculate, if you’re doing it in your head, is to simply divide the total number of miles covered by the total number of minutes it took you, then multiply this result by sixty, to give you your average speed in miles per hour. So, for example, if you take twenty minutes to cover nine miles, your average speed will be (9 / 20) x 60, or 27 mph.

Example Journeys

It’s advised that you take a break every two hours driving. Many people extend this - for a three hour trip, I’ll usually not bother stopping, but if it is likely to extend into four hours, I’ll stop at the mid way point.

The effects of a stop on a journey can make a comparatively large difference to the average speed. For an example, when I commuted from Norwich to York, I would leave Norwich at 04:30 on the Monday morning, and leave York at 15:00 on the Friday afternoon. I drove at the speed limit.

I had a choice of two routes - the A1 route (via Newark, then the A17, A47 or B1145 to Norwich). The other route took me through Lincolnshire, via Horncastle and the B1192 /cough/, and also used the M180.

The A1 route was quicker on the Monday mornings, primarily because it was quiet and I was able to cruise at 70 unhindered. It was slightly further - 205 miles. However, if I did the trip non-stop, I would be parked outside the office at 07:45 - just three and a quarter hours, for an average speed of 63 mph. If I stopped, it invariably added another fifteen minutes to the journey time, so the average speed dropped to 58½ mph. Still, that’s not bad going.

On a Friday evening, as you might imagine, the A1 gets clogged up. What made it worse were the roadworks at Newark. I only tried the A1 route south once, and the overall trip took me five hours, forty minutes - an average speed of just 36 mph. On this occasion, I didn’t leave York until 16:30. The main reason for the long trip was that it took me one and a half hours to reach the M62, thanks to York being very busy and there being a significant hold up at Selby. After this trip, I refined my route to avoid the traffic black spots.

Going via the Lincolnshire route did take longer in the morning - three and a half hours to cover 196 miles, for an average of 56 mph, but on the way back south on a Friday night, the trip took much less time. The fastest I did the run home was a single stopper, in four hours, fifteen minutes, for an average speed of 46 mph. That’s still considerably slower than the drive to York, but the main reason for this are that the primary route to Norwich from Lincolnshire - the A17 and A47 - is mainly single carriageway, busy, and consequently sluggish. The single stop was an emergency pee break!

A good example of long haul average speeds can be found in the Italian Job Road Trip article.

What Slows You Down?

There are several things that can extend journey times. Discretionary stops - for fuel, to stretch your legs, or get food - can make a big difference. They’re important, of course, and you should never not stop just for the sake of managing a decent average speed!

Road works and traffic jams will, of course, extend the journey. You can avoid traffic hold-ups by picking an alternative route. On quiet roads, the average speed will not vary much depending on what time of day or night it is, except in bad weather. It will be slower than a primary route when it is quiet, but usually quicker when it is busy. They’re also a break from monotonous driving on a motorway or dual carriageway.

Bad weather also slows you down, both directly and indirectly. Clearly, if it’s snowing, icy, foggy, or there’s a heavy rainstorm, you (shouldn’t) won’t be driving so quickly. Indirectly, when the weather is bad, more people take their car. This is most obvious in a city.

The time of the day: this is linked with congestion. Avoiding schools between eight thirty and nine thirty, then between three and four, is a good idea. It does vary across the country, but it tends to be busier on a Monday morning compared to the rest of the week, and again busier on a Friday evening compared with the rest of the week. Before nine on a Sunday morning is a good time to travel. The Fridays before a bank holiday are also busy.

Speed limits can also slow you down. This is obvious enough. Sticking to main, national speed limit roads will give you a higher average speed than driving through every town and village. However, there will be times when it’s quicker to drive through a country road than to drive along a congested motorway.

Getting lost is not only annoying but it can make a big difference to your average speeds. Ten minutes in the wrong direction adds twenty minutes to your journey if you have to double back on yourself. Proper planning is essential to a long drive even if you happen to have a GPS navigation system.

DervMan’s Tips

Try to avoid time pressure: our trip from York to Bournemouth (documented here) had a small element of time pressure. We needed to average 50 mph across the leg south. Now even though we were using the motorway, this did give us some pressure – which is best avoided!

Check your fuel level: unless you know the route well, try to avoid having to make a fuel stop mid-route, simply because Murphy’s Law states that when you need fuel, you’ll be forced to either use a busy, or an expensive garage (or both), or - worse - you’ll have to detour to get fuel. Sometimes, stopping en route is unavoidable (your car may not have adequate range for the trip), in which case, plan when you are going to buy fuel but give yourself plenty of leeway. For some trips – such as the Italian Job Road Trip – it’s difficult to plan your fuel stops so if you want to make good time, try to stop for fuel when you stop for other reasons, like food.

KaKam

Travel when traffic is light: another obvious one, really. I was given the opportunity to get to work at about ten o’clock rather than eight when I was commuting from Norwich to York. However, I reasoned (correctly, I have since discovered) that the trip would take me longer if I left Norwich later. Essentially, if I left Norwich at 06:00 rather than 04:30, the trip would have taken between four and four and a half hours. That’s another hour driving! I expect that if I had left York at seven o’clock on the Friday evening, rather than three o’clock, the trip would have taken a similar time.

Check your route: it’s pretty simple, but if you’re going to a part of the United Kingdom that you don’t know, check your route. I use Multimap as a good site for directions and route planning, and AutoRoute, but I always back it up with a paper road atlas. Also, check for traffic problems - a good way is to use Usenet, because there may be people who actively use that route and who can suggest alternative routes and diversions. You can also check out sites such as the AA, use Orange’s TrafficMaster service via WAP, and listen to local and national radio broadcasts. The alternative to the “hard work” of the above (it’s not hard work, heh) is to invest in a GPS navigation system.

To plan a long journey, a ballpark average speed all any given roads is the speed limit, less 10 mph. So if your trip is 200 miles, of which 100 is main roads, 80 is motorway / dual carriageway, and the remaining 20 is in a city, your calculation would be as follows:

Motorways - 80 miles @ 60 mph will take us 80 minutes.

Main Roads - 100 miles @ 50 mph, takes us 120 minutes.

Urban: 20 miles @ 20 mph will take us 60 minutes.

Total: 200 miles in 260 minutes, or four hours, averaging 46·2 mph.

Whilst it will not work for all journeys, for a long trip it does seem to be reasonably accurate with the exception serious traffic problems. I calculated that we ought to be able to average 50 mph on the drive from York to Bournemouth using the above formula. I calculated this from 250 motorway miles, 30 main road miles and 20 urban.

Finally, if you are able to, share the driving: two people can usually cover a greater distance if they share the driving. This is more important if the driver is not used to such long drives, and it is quite possible for concentration to lapse.