Different speed limits apply to various states. Where in one stretch of highway in Texas permits driers to drive to a maximum speed limit of 85 mph the max speed limit in highways across Minnesota has increased from 55 to 60 mph.
Now, one might wonder as to why there is such varying speed limit across different states. Well, the speed limit is actually determined by how the road is classified.
TYPES OF ROADS
There are three general classifications of road types:
- Arterial- These types of roads have highest speed and fewest access points.
- Collector- These have more access points and have higher speed.
- Local- These have a low speed limit but high access points.
If you notice one trait then it is this- Where the access point is low, the speed limit is high and where the access point is high, the speed limit is low. So, it is to be noted that these factors are inversely proportional to each other and this is exactly what determines the speed limit.
Roads that have fewer intersections and fewer travellers moving perpendicular to each other have the condition in which they can sustain a higher speed limit. It will still be considered safe!
Roads with relatively higher number of intersections also have more bikers, cyclers and pedestrians travelling across various directions at various speeds. This cluster and to and fro motion leads to greater chances of accidents and therefore calls for preventive measures such as low speed limit. This is why driver feedback signs are provided in key areas to alert drivers about speed limit and maintain it.
It is to be noted that while speed limit is being reduced and traffic coordination measures are being optimized on various local roads, an increase in speed limit has been seen on interstate roadways in various parts of the country. Although both these cases may seem at odds with each other, the reason for both is the same, concern for safety.
WHY DO SPEED LIMITS CHANGE?
Speed limit changes are made as a result of a study over a period of time. A public agency is responsible for conducting spot speed study which documents the speed of individual vehicles that pass by on a specific road. The data collected is then plotted on a chart and is evaluated. Through this study, the actual speed of vehicles that pass by is found out.
The average speed at which 85% of the vehicles drive by at is considered as prevailing speed and then this is determined as the speed limit. This is because that is the safest speed noted without any accidents. A variable message sign is used to denote speed limit and other road related information at key junctions and road spots.
Say, there are two cars moving down a road, one at a low speed and one at a very high speed. This can actually pose a major threat to the safety of other vehicles on that road. A slow vehicle and fast vehicle by themselves are not dangerous since these are relative but turn dangerous with respect to other vehicles on the road. This is why the 85% is a good percentage to consider for determining a speed limit and filtering out the drastic exceptions.
So, to adhere to the prevailing speed, speed limit changes are made from time to time so that this lessens the chances for accidents. Solar vms signs are used at key spots on specific roads because they serve dual purpose. They not only run on solar power thus reducing electric power consumption but they also do not need to be changed with change in speed limit thus sparing the cost of installation.