Friday, January 09, 2009

Forgotten factor-Safe Braking Distance

Parents often advise children- “go slow- don’t drive fast”. We see lots of sign boards which tells you not to cross a particular speed limit. On a straight clear road when driver speeds up, others ask him to slow down. In brief, there is a general belief that driving slow is a the best way to avoid accidents. Our traffic police have interceptors on highways to catch speeding vehicles and fine them… While driving slow helps, there is another important factor, which most of us never give importance to (or may not even be aware of). It’s called Safe Braking Distance (SBD).

Safe braking distance is the minimum needed empty distance ahead, needed for the vehicle to come to complete halt without bumping into vehicles ahead, from its current speed, from the moment an emergency occurs. In other words, SBD is the distance you’ve to maintain, between your vehicle and the vehicle behind you, so that your vehicle can be safely stopped in case of emergency.

How do you measure Safe braking distance?
Primarily, SBD is a function of speed at which you’re cruising. Higher the speed, more will be the distance required to stop the car. Normally, for a decently skilled driver, on a normal road, it will take about 100 meters under normal condition to stop a car from 100 kmph (that is on a dry road. Can be twice or thrice that distance for wet road) and distance increases exponentially with increase in speed. But then, one can’t physically measure the distance while driving and will have to rely on his/her judgment to assess if the available distance is enough. Also the distance required to stop depends on dozens of parameters, detailed below.

One should maintain additional Safe braking distance if

  • It is night time
  • The road is slippery due to rain/snow/loose gravel
  • There is no road divider to separate oncoming vehicles
  • The road is curvy or visibility is affected due to fog or other factors
  • The driver is not skilled/experienced/confident enough
  • Vehicle doesn’t have ABS (ABS may not significantly reduce the breaking distance but it mainly prevents vehicle from skidding and gives better control/confidence to the driver)
  • Driver is less attentive (either due to alcohol consumption or he’s listening to music or talking with co passenger/on mobile etc) as this increases response time and vehicle would have cruised several meters before the driver comes to his senses and applies the brake.
  • The manner in which the vehicle ahead is being driven (if it is being driven rashly or stops/slows down abruptly etc)
  • You’re not regular on that road and not fully familiar with the road terrain (if there’re abrupt speed breakers or bad stretches on an otherwise good road, drivers miss to notice the hump/bad stretch till they come very close- this means abrupt stopping and vehicle behind may not anticipate it and ram from behind- live example, see the photo- Innova caught by surprise and bumps into the truck as truck suddenly slowed down due to bad road
  • The condition of the vehicle ahead is not good (no working tail lamps, worn out tyres/visibly aged vehicle etc- most our Indian trucks may not have their tail lamps and break lamps working, even if they are working, they may be covered with mud or may not be visible due to broken glass-this means, during night time you’ll not notice the vehicle till you move very close)
  • There’re no free additional lanes at left or right (if you don’t have a space to go, only option will be to ram into the vehicle ahead)
  • There’s no fencing and possibility of stray animals, people crossing the road is very high
In my opinion, maintaining safe braking distance is more important that going at slow speed. I don’t see any harm speeding if the road is straight, empty and has full visibility, provided the driver is in his full senses to anticipate any signs of trouble and can slow down in time.

While we usually maintain some distance from the vehicle in front of us, it is also critical to keep an eye on the vehicle on your tail, unless you enjoy being bumped in the back. But while we can slowdown and increase the distance between our car and vehicle ahead, it may not be possible to tell the car behind you to maintain the gap. If you suspect the distance is too close, best will be to let that car overtake and pass.

I had a similar experience last month on 28th December- While driving from Shimoga to Bangalore, I had a cat and mouse chase with 2 other Swift cars (all 3 were Swift VDis, mine Copper Red colour, other two were white and blue ones). I enjoyed the chase for a while, but eventually slowed down as road condition was not that encouraging. The other 2 cars continued the race. Few kms later, we spotted these 2 swift cars parked on the road side with drivers talking/arguing with each other. There was a speed breaker and when the car ahead (blue one) braked abruptly, the white Swift which was on the tail couldn’t anticipate this and before it could be stopped, it had given a deep kiss to the blue swift ahead. There weren’t any casualties, but the dent to the brand new car was clearly visible. Later I spotted the car at Kamat restaurant outside Tumkur where we’d stopped for dinner- I took a photo of the car but the owner came out and insisted that I delete the photo and I had to honor his request.

I spotted a more serious collision the next day while driving from Bangalore to Chennai, via Chittoor and Ranipet. The photo you see in this post is taken during that drive, where truck driver stopped/slowed down abruptly due to bad road and Innova rammed into it from behind. The wind shield had a severe crack but hadn’t shattered into pieces. I believe this version of Innova came with airbags (both passenger side and driver) and hope the occupants didn’t suffer any major injuries. After observing these 2 incidents and noticing that we hardly give any importance to the concept of safe braking distance, I felt like writing this post.

Your thoughts welcome.

Photos by Krishna Shastry


hari said...

Yes, it's very important. Unfortunately in India, we hardly bother about safe braking and so on and so forth. And in the cities it's even worse, with bumper to bumper traffic even at speeds as high as 40-50 kmph (which is quite high in crowded areas).

Mridula said...

I am known for maintaining a distance but then the problem is that a vehicle will overtake me barely and try to squeeze in the distance that I am trying to maintain. And it has happened only once but a guy on a motorbike bumped my car from behind because I had to break because of a tempo breaking ahead of me!

Siva said...

A very important point indeed! One of my friend rammed his Santro into the rear of a lorry at very slow speeds when he was returning from chennai to Bengaluru. Luckily nothing happened to them but the car needed major repair. He was sleepy at the wheel. I take 30 Min rest when i feel sleepy. Also when driving at night on long journeys follow the left edge of the road for reference. if you try to follow the center line on a two way road you get lot of glare from oncoming traffic and you tend to go in the direction of your sight which can be very dangerous.

Radhika Ganesan said...

I could not imagine a life without my scooty when i was in Nagpur but when i shifted to Pune, i had to do without it because i didn't have the papers and NOC of my scooty! I recently drove a two wheeler in Pune, and i was so scared as i am not used to so much of traffic that i was driving at a very slow pace and my friend was constantly asking me to inc. the speed but i thought its better to be safe than sorry ! Poor she ! :):)

Shrinidhi Hande said...

@ hari- if you try to maintain some space in city driving, a bike or auto will come and squeeze into that space..

Shrinidhi Hande said...

@ Mridula
Yes, motorbike riders are usually more casual at times than a car driver, and some such riders are alive only because rest of the road users are accommodative of their rash and careless driving

Thanks for sharing your experience..

Nagpur and Pune are both within a same state right? we still need NOC for moving vehicles ? I think they're required only when you move them from one state to another...

Good that you drive slow and carefully.

hari said...

Good point about bikes and autos - major headaches for car drivers who are caught between the big bully buses and the pesky autorickshaws and two-wheelers.

Ms M said...

Most people will try to get ahead of the car leaving the gap in the front in city limits. But def a good idea on roads with less traffic. There is no point in tailgating and in the US a tailgater can get a ticket for this. As more people start driving the cheaper cars now avlbl India, new drivers will get into more crashes because of ignorance. You write such thoughtful posts and I had only 1 complaint here.
I must object to your writing about driving under the influence . Even a couple/few drinks can lead to impaired judgment, and DUI is treated very casually in India. Please do consider this in your future posts.

Shrinidhi Hande said...

Ms M,

Appreciate your comment...

Abt driving under influence, I do not consume alcohol and hence do not know if it takes one glass or ten to take one to impaired judgement... But the person at the wheels must be knowing if it is not safe to drive due to what he has consumed. Where am I wrong in this?

Ms said...

The driver does not know it is unsafe because we all support the myth that a few drinks are ok. If we all start saying "even 1 drink is too much" then the attitude may change. Like when a group of people have been drinking, there is no designated driver, who abstains and then drives everyone home safely.
Even texting or fiddling with controls is a bad idea and should not be tolerated. But while one can immediately stop texting and just focus on the road, dui means the driver needs hours to regain focus. Hotels should speak up and tell the customers that they are drunk and should not be driving and in the US, bartenders do this to avoid liability issues. Friends should just decide to take a taxi back . This was what I meant when I said we should all stop tolerating bad behavior. A driver cannot control bad road design, weather and other's faults but s/he can manage personal responsibilities which pt # & covered.

Shrinidhi Hande said...

OK. Thanks for the clarification. I agree

joseph said...

In the definition you have mentioned it is safe distance that you need to keep from the vehicle on your rear side. That is only partial you need to keep the same distance from the vehicle that is running infront of you as well which is more important. when a car chases you from behind you will have to speed off to keep the safe breaking distance, that is not advisable. instead of that you give way for the vehicl behind keeping the speed limit to that is prescribed for the road.

Joseph J K, Doha, Qatar

Shrinidhi Hande said...

Dear Joseph,
Appreciate your comment. I didn't say SBD to be maintained with rear vehicles only.

(Ref: "While we usually maintain some distance from the vehicle in front of us, it is also critical to keep an eye on the vehicle on your tail, unless you enjoy being bumped in the back".)

Yes, it is critical to maintain distance both on front and rear and makes sense to give way to fast moving vehicles.


Anonymous said...

On Friday, Oct. 23, 2009, a friend was killed while following an Ambulance to closely. The ambulance, which was transporting her mother, had to swerve to avoid an oncoming auto. My friend did not have time to react. Both drivers died at the scene.

I teach driver's education and I plan to share your info with my class.

Thanks for posting it.

Shrinidhi Hande said...

That was Sad. Where did this incident happen?

Anonymous said...

Very interesting. Thank you.