One should always maintain speed which he can handle, and never try anything putting others' life at risk. The quote illustrates this:
"Baseball is like driving, it’s the one who gets home safely that counts."
The car means everything related to car – both in terms of design and shape, which allows or does not allow this particular car to drive at this particular speed. And this does not mean that car just can reach this speed, it means the car can maintain this speed with reasonable three-dimensional stability under given environment. It is not about engine at all (we have a joke in Russia: even a wardrobe can reach 200km/h if you let it slide down a big mountain), it is all about tires, suspension, steering, body stiffness - active safety in other words.
I see that this calls for more information: Statistically, the faster the speed, the greater the risk. However, when speed is increased there is a certain balance: With increased risk comes greater hazard perception and better concentration, and a better flow relative to the traffic around us. On the other hand, the sharpened focus is not likely to last as long, and the flow of traffic might be disturbed if you drive faster from the average speed around you.
Therefore, the speed to drive at is never any fixated figure but rather the speed that suits the conditions. This speed changes, often every few seconds, and also slightly changes from driver to driver and from situation to situation (on the same road). It is related to all levels of driving: The driver, the car, the road and the traffic:
- The Driver: How focused and alert is the driver?
- The car: How well maintained is it? At what speed does it remain economic in terms of wear and milleage?
- The Road: What is the road surface? What are the road conditions? How wide is the road?
- The Traffic: How thin is the traffic? What is the general flow speed of it? What vehicles does it consist of?
To judge speed currectly we need to apply a principle I have formerly described as the most important element of driving: Observation and Anticipation. We need to look to the furthest distance possible and not on the mid-range, but at the horizon, down the road. Now, we need to adjust our speed according to the two golden rules:
1. "Be able to stop WELL within the distance one can see to be clear, and the one knows would remain clear."
2. Be able to plan at least seven seconds ahead.
Let's review the first golden rule: If I was driving at an open highway, with thin traffic and a well-paved surface, on a well-maintained car and with normal levels of concentration, and my field of vision was to be 1000 feet ahead, I should have adjusted my speed so that, in any case, I could stop within about 80% of that distance (800 feet). Of course in real life this is not a mathematical calculation but a skillfull estimation, which gets better with experience.
If I was driving on a busy city street, I would have to drive significantly slower than described above: The tarmac is not likely to be as good and the field of vision ahead is going to be much shorter. Furthermore, in many areas, we can except to negotiate hazards that appear not only far ahead, but suddenly appear in the mid-range. We need to know that the area will remain clear. Otherwise, we have no choice but to further reduce our speed so we can stop with 60% to even 10% of the distance we see to be clear.
This brings us to the second rule: We need to maintain a minimum of two seconds gap from the car in front and behind (assuming dry conditions, maintained car and good concentration), but we need to look past the car in front and plan further ahead. You need to have at least seven seconds between yourself and the current limit of your visual field.
To further elaborate, our speed -- and likewise other variables like the level of alertness and our position on the road -- depend on an estimation that we make, based on a very vast amount of variables:
- The driver: How concentrated? How alert?
- The Car: What kind? Is it a truck or a sedan? How well maintained?
- The road: What road? Is it a highway, a two-lane roadway or a residential street?
- The traffic: What traffic? Other cars? Trucks? Bikes? How tight is the traffic? What is the speed of the cars around me?
- Length of the road: How far ahead can you see to be clear?
- Width of the road: How wide is the road? How many lanes? Is there an open, hard shoulder on BOTH sides?
- Road Surface: Is it tarmac? Is it concrete? Maybe dirt, or ice? What is the quality of the tarmac? Is is gry or black? Is it abrasive or shiny? Is it bumpy or smooth?
- Road Conditions: Is it wet? How wet? Is it greasy? Is there dirt on the pavement? How hot is it? Maybe there is snow or ice?
- Guardrail: Is there a guardrail? What kind?
- Shoulders: Is there a hard-shoulder? Is it on both sides? How wide is it? Is there a "soft" gravel shoulder? How wide is it? What is the height difference between it and the road?
- Road fomation: Is it a two-lane roadway or a highway? Is there a median? Is it a one-way residential street? Maybe it's a tight rural road or a winding mountain road?
- Road direction: Is it going uphill or downhill? How steep is the incline? Is there a turn? How sharp does it seem? Is it a blind corner?
- Typical Hazards: What hazards do you anticipate on this road? Do you anticipate children around a school? Do you look for oncoming vehicles on a two-lane roadway?
- Immediate hazards: What immediate hazards do you see? Is there is anything that might happen and put you at risk? Maybe there is a car stalled on the shoulder of the road? Maybe there is a colum of parked cars near the curb, where one car might pull out suddenly or hide a child?
- Safety bubble: What is your safety margin? How far are you from the car ahead? How far are you from the car behind? How far are you from cars alongside you?
Let's take a casual highway: I'm concentrated and my car is well maintained. I'm driving a sedan. I can see far far ahead. There is thin, fast moving traffic of light cars. The road is well paved, made of dark-shaded and seemingly abrasive tarmac, which looks dry and clear of grease or dirt. There is an advanced type of armco to the right and a concrete median to the left.
The road is very wide, with three lanes in each direction, a small left hard shoulder and a wide right hard shoulder. It's leveled and straight. The typical hazards on this kind of road are about tailgaters, swerving cars and stalled cars along the road. I keep two seconds clear from the car ahead, ensure that no other driver is tailgating me and stay away from stalled cars, while always keeping the lane/shoulder clear to at least one side of my car. These are conditions for driving which is quite fast.
The next step is a two-lane roadway: The tarmac is of medium quality and covered and dust. There are two lanes but the shoulder of the road is made of gravel, and is lower than the road surface, albeit wide enough to still be considered as a possible escape route. There is thin traffic and I can maintain a safety bubble 360 degrees, and the forward vision is quite clear to a distance of at least 700 feet ahead. There are oncoming vehicles and a risk of a head-on collision. This is also a fast road, but it cannot be driven nearly as fast as the highway.
Now let's look at a main road in the city: There are three lanes in each direction, but the tarmac is a bit less good and seems greasy. The road is less wide and the forward field of vision is about half. There are no shoulders or guardrails, but rather curbs on both sides of the road. The traffic is more dense and also includes bikes, mopeds and what not. I keep two seconds in front, two behind and try to stay away from driving paralle to another car, since I have no escape route to the other side. The typical hazards are much more versatile and can include pedstrians in the mid-range, cars stopping suddenly or pulling out at you. These conditions force a significantly reduced speed, although a conservative pace (of, say 30mph) can be maintained.
The next in line is a tight residential street: There are columns of parked cars along the sides, pedestrians on the pavement to both sides and a car in front and behind, with two lanes, one to each side. There are typical hazards from an oncoming vehicle, a parked vehicle pulling out or a pedestrian suddenly bursting into the road. The vision and consipicousness of the vehicles is also somewhat reduced by driving the shade of the buildings. This road is due to be driven quite slowly, a would dare say at below 20mph.
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