Safe Speed Forums

Nevertheless, it still puts the lie to "Speed Kills".

Both views support the fact that the seminal research underlying the Solomon curve shows that the greater the difference between a driver’s speed and the average speed of traffic – both above and below that average speed – the greater the likelihood of involvement in a crash.

Thanks. That article does point out that the low speed part of the curve is badly distorted by accidents involving vehicles entering or leaving the road.

Not really.
It just puts another phrase into the equation: Different speeds kill.
You'll note the upward sweep of the curve, which seems to be parabolic (I would have liked the high speed range to have been investigated more), showing that higher speeds have more accidents as well.
Slower speeds kill as much as faster speeds, the parts you should be paying attention to are those that infer that drivers whose speed differs from that of the majority (whether fast or slow) are more likely to have (or be involved IN) accidents. And it does not necessarily have to be either the fast or slow driver at fault.
The most you can infer from the solomon curve is stated in the wiki entry:

So, speed does kill (both high and low)

The obvious conclusion from the graph is that, at least on non-urban roads speed limits should have both minimum and maximum components. Driving on 55mph limit freeways in the USA where every vehicle, commercials included, is traveling at the same speed always made me feel very safe. And the main thing that worries my visitors from over there is what they see as massive speed differentials on our motorways.

traveling at the same speed always made me feel very safe.

Thanks. That article does point out that the low speed part of the curve is badly distorted by accidents involving vehicles entering or leaving the road.

so for the safest option the speed limit should be set at the lowest point on that curve ?
i.e. the speed the majority of drivers would be travelling at.

this does seem to back up to an extent the 85% guide for setting a speed limit... rather than choosing a random (low) limit which means someone sticking rigidly to it might be introducing differential speed to the rest of the traffic (?)
(ok the limit is likely to influence but not necessarily dictate the majority choice of speed and i imagine the further the limit is from the majority normal choice the greater the problem)

If you read Soloman properly the lowest crash risk is for those at the 85% showing that the slightly (say up to 20 mph) faster than average is the safest. Soloman used free speeds ie where there were no artificial constraints eg slow traffic and of course in his day there were no cameras or even radar

· The majority of motorists drive at a speed they consider reasonable, and
safe for road, traffic, and environmental conditions.
· Posted limits, which are set higher or lower than dictated by roadway and
traffic conditions are ignored by the majority of motorists.
· The normally careful and competent actions of a reasonable person should
be considered legal.
· A speed limit should be set so that the majority of motorists observe it
voluntarily and enforcement can be directed to the minority of offenders.
· A driver’s choice of speed can impose risks on other road users. Crash
severity increases with increasing speeds because in a collision, the amount
of kinetic energy dissipated is proportional to the square of the velocity.
Crashes, however, appear to depend less on speed and more on the
variation in speeds. The likelihood of a crash occurring is significantly
greater for motorists travelling at speed slower and faster than the mean
speed of traffic.
· Maximum speed limits are set for ideal road, traffic, and environmental
conditions.
· Establishing safe and realistic uniform speed zones is important because it
invites public compliance by conforming to the behaviour of the majority of
motorists and provides a clear reminder to violators. It also assists the
courts by providing a guide as to what constitutes a reasonable and prudent
speed and reduces arbitrary enforcement and conviction tolerances.

The original research does account for it:


Even without the slow 'turners', the crash risk for slow drivers is still huge.

But according to the graph the risk is higher for faster drivers.
The risk in the chart is for turning drivers, which is not slow drivers but drivers going slowly. A different thing altogether.
Relative involvement rate for slow speed is 6-, for high speed 6+.

Even excluding turning crashes, the crash risk for vehicles traveling much faster or slower was six times the average rate.

But according to the graph the risk is higher for faster drivers.
The risk in the chart is for turning drivers, which is not slow drivers but drivers going slowly. A different thing altogether.
Relative involvement rate for slow speed is 6-, for high speed 6+.

Not really.
It just puts another phrase into the equation: Different speeds kill.

Exclusion of "turning" accidents dramatically alters the state of play.

You (I) would always expect a higher amount of accidents on a road, or roads, which feature a mix of slow/fast vehicles.
Turning accidents feature highly because many drivers fail to see vehicles slowing to turn and brake harshly to avoid collision. Seen it loads of times. Especially those slowing/stopped to turn right. It does not mean that the slowing/stopped drivers were at fault.

If a person cannot overtake safely, they should not overtake.

blaming a lorry/van/car for causing an accident by being slower (either by observing the speed limit or just being unable to go faster) is not helpful.

Let me make it clear - you should ALWAYS reduce your speed when driving at NIGHT.

Twisting country roads.

• During the day, I drive at a slower safe speed around corners in case some over enthusiastic chap is coming the other way in the middle of the road.
• During the night, I can see oncoming car's headlights before I see them so can take these corners at an increased safe speed when clear.

There are many other examples.

How so? The overall point is still valid: slow drivers are involved in more crashse than drivers who just go with the flow. This was the point: "The slowest 30% have the highest crash risk" - which is almost true as far as this debate is concerned, perhaps it should be:
"The slowest 30% have the joint highest crash risk".

Unfortunately animals and people don't normally have powerful headlamps so the lack of visible lights does NOT mean that the road is clear. So the safe speed is not increased at night.

Ok, you can blame unnecessarily slow drivers (those with no reason for going slowly) for some accidents. But you cannot blame those going at the maximum speed allowed by law (when those are lower speeds than other traffic is allowed to drive) for accidents.

there is always going to be slower traffic.

If a driver gets frustrated by slower traffic then maybe that frustrated driver should not be driving,