Arrive Alive

Stopping Sight and Driver Reaction Time

Stopping Sight Distance

S=dr+db

S=stopping sight distance
dr=driver reaction distance (decision distance - combined observation, identification and decision distance)
db=braking distance (action distance)

dr=v.tr

db=(v*v)/(2g(f+-G))

v=speed
tr=driver reaction time (varies from 2,5 to 2,8sec)
g=acceleration of gravity
f=coefficient of friction between tyres and pavement (varies with speed – for wet, glazed asphalt it varies from about 0,45 at a speed of 10km/h to 0,2 at a speed of about 70km/h)
G=average grade

The above distances depend on whether a vehicle goes into a skid or not – distances increase drastically when vehicles go into a skid.


 

 

The type of vehicle (vehicle mass – together with speed relating to momentum) also plays a role – for example : in emergency situations a light passenger car doing in the order of 100km/h needs about 60m to stop, a truck weighing less than 5t would require about 70m and a truck weighing between 5t and 10t would require in the order of 80-90m (both doing about 100km/h). (In all these cases vehicles do not go into a skid situation and distances given do not include driver observation and decision distances).

Speed plays a major role in driver observation, recognition, decision and reaction time. In the case of a hazard or an incident on the road, the driver of a medium size motorcar driving at a speed of 120 km/h will need a total distance of about 227 metres from the point of observing a hazard and taking evasive action until the vehicle comes to a standstill. For a driver driving at a speed of 180 km/h this distance more than doubles to about 480 metres. Information on the total observation, recognition, decision and reaction distances required for various sized motorcars and speeds on a flat section of road are given in the graph below.

 

 

Required Stopping Distance - metres
Decision distance plus Action distance
Speed
km/h
Small
Car
Medium
Car
Large
Car
Heavy
Vehicle
60 60 66 77 116
70 78 86 101 154
80 99 109 129 197
90 121 135 159 246
100 146 163 193 300
110 174 193 230 359
120 203 227 271 424
130 235 263 314 495
140 269 301 361 570

 

 

Required Stopping Time - metres
Decision Time plus Action Time
Speed
km/h
Small
Car
Medium
Car
Large
Car
Heavy
Vehicle
60 5.73 6.44 7.76 12.37
70 6.50 7.32 8.87 14.24
80 7.27 8.21 9.97 16.11
90 8.03 9.09 11.07 17.98
100 8.80 9.97 12.18 19.86
110 9.56 10.86 13.28 21.73
120 10.33 11.74 14.38 23.60
130 11.09 12.62 15.49 25.47
140 11.86 13.51 16.59 27.34

 

Also View:

Brakes/Braking and Road Safety

 

Search Road Safety Articles

Latest Pages

Trauma Counselling and first responders / paramedics

Trauma Counselling and first responders / paramedics

With the daily carnage on the roads of South Africa, it is not only the victims of road crashes that are exposed to trauma. Our first responders to these road crashes such as paramedics and members of the police are exposed to the trauma of horrific crashes and it is important that the long-term effects

Read More

Driving in Winter / Driving on Snow and Ice

Driving in Winter / Driving on Snow and Ice

Driving in winter may be hazardous for the unprepared and inexperienced driver. Although South Africa is not as well known for extreme winter conditions, such conditions may be extremely hazardous and many drivers might need to consider measures relating to the condition of their car as well as driving

Read More

Emergency Response Time and Response to Road Crashes

Emergency Response Time and Response to Road Crashes

Few road users are aware of the factors that could determine the time needed to respond to a vehicle accident. It is important for road users to be aware of these factors as well as steps that they can take to assist emergency teams in responding swiftly to accidents. Emergency response providers have

Read More

Safety when Witnessing and Reporting Crime on the Roads

Safety when Witnessing and Reporting Crime on the Roads

We sadly experience on our roads, not only threats from irresponsible and bad drivers but also threats to life and property from criminals targeting road users. Nearly every day we are warned of or hear about a protest action on a road somewhere, a hijack or a cash-in-transit robbery. On the Arrive

Read More

Safety and Safe Driving in Areas of Public Violence

Safety and Safe Driving in Areas of Public Violence

Introduction South Africans have in recent months experienced many traffic delays, disruptions and at times total road closures brought about by protests, riots and incidents of public violence. These protests were related to service delivery, education issues, politics and several social issues. It

Read More

Crime as a Threat to Road Safety in South Africa

Crime as a Threat to Road Safety in South Africa

South Africans live in a country blessed with beauty and diversity. We share a country with a colourful history having overcome rather significant and unique challenges. However proudly South African, we may be, we have to admit that we face serious challenges to safety daily at our homes, places

Read More

Load More Pages

Partners

View All