In transport, driver visibility is the maximum distance at which the driver of a vehicle can see and identify prominent objects around the vehicle. Visibility is primarily determined by weather conditions (see visibility) and by a vehicle's design. The parts of a vehicle that influence visibility include the windshield, the dashboard and the pillars. Good driver visibility is essential to safe road traffic.
Blind spots may occur in the front of the driver when the A-pillar (also called the windshield pillar), side-view mirror, and interior rear-view mirror block a driver's view of the road. Behind the driver, there are additional pillars, headrests, passengers, and cargo, that may reduce visibility. Blind spots are affected directed by vehicular speed, since they increase substantially the faster one goes.
Forward visibility
This diagram shows the blocked view in a horizontal-plane in front of the driver. The front-end blind spots caused by this can create problems in traffic situations, such as in roundabouts, intersections, and road crossings. Front-end blind spots are influenced by the following design criteria:
• Distance between the driver and the pillar
• Thickness of the pillar
• The angle of the pillar in a vertical plane side view
• The angle of the pillar in a vertical plane front view
• the form of the pillar straight or arc-form
• Angle of the windshield
• Height of the driver in relation to the dashboard
• Speed of the opposite car
Effects of A-pillar angle on visibility
Most passenger cars have a diagonal pillar as shown in this side view. The angle between the horizon and A-pillar is approximately 40 degrees with a straight pillar that is not too thick. This gives the car a strong, aerodynamic body with an adequately-sized front door.
Panoramic windshield
The sides of a panoramic windshield are curved, which makes it possible to design vertical A-pillars that give the driver maximum forward visibility. However, it is impossible to design an aerodynamic small car with a vertical A-pillar because the more vertical the A-pillar is, the less space the door opening has, and the greater frontal area and coefficient of drag the vehicle will have.
Examples of cars with an almost vertical A-pillar:
• Honda Step Bus Concept
• Saab 900
• School bus
• Almost all Cadillacs from 1954–1959
Flat windshields
Some modern car designs have an extremely flat A-pillar angle with the horizon. For example, the Pontiac Firebird and Chevrolet Camaro from 1993-2002 had a windshield angle of 68° with the vertical, which equals just 22° with the horizon.
A flatter A-pillar's advantages include reducing the overall drag coefficient and making the car body stronger in a frontal collision, at the expense of reducing driver visibility in a 180° field of view from left to right.
Other disadvantages of a flat windshield angle
• Other traffic can not see the driver through the reflection if the driver can see them.
• The heater needs more time to heat the bigger window surface.
• The flat windshield angle does not let snow slide off easily.
• The driver cannot reach the whole flat window to clean it easily.