Car accidents fall into several major categories (whose names are self-explanatory):

* Rear-end collisions
* Rollovers
* Head-on collisions
* Single-car accidents
* Pile-ups
* Railroad crossing accidents

The term level crossing (also called: railroad crossing or grade crossing) is a crossing on one level (or "at grade") - without recourse to a bridge or tunnel - used to describe the crossing of a railway line by a road, path, or other railroad.

It also applies when a light rail line with separate right-of-way (or a reserved track tramway) crosses a road; the term "metro" usually means by definition that there are no level crossings (i.e. that the system is grade-separated).

About Rail Crossings

In the United States, and in countries following US practices, a train must have a bright headlight, and a whistle or horn must be sounded as the train approaches the crossing. Some American cities, citing noise pollution abatement, have passed laws prohibiting the sounding of bells and whistles, however their ability to enforce such rules is debatable. In December of 2003, The US Federal Railroad Administration published regulations that would create areas where train horns could be silenced, provided that certain safety measures were put in place. More information can be found at the FRA website at and following the page link under 'Train horn rule.' The regulations were scheduled to go into effect in December 2004.

All crossings in the United States are required to be marked by at least a crossbuck. Most crossings that intersect rural roads have this setup. As traffic on the road crossing or the rail crossing increases, safety features are ramped up accordingly. More densely populated crossings have alternately flashing red lights to warn motorists, and a bell to warn pedestrians. Additional safety is attained through gates that block motorists approach to the tracks when activated. Increasingly, crossings are being fitted with so-called four-quadrant gates, with a gate mechanism on either side of the tracks for each direction of automotive traffic. The exit gates blocking the road leading away from the tracks in this application are equipped with a delay, and begin their descent to their horizontal position several seconds after the entrance gates do, so as to avoid trapping highway vehicles on the crossing. Four-quadrant gates prevent vehicles from driving around lowered gates to try to beat a train.

A track that will run high-speed trains in excess of 120 mph (193 km/h) is being tested in Illinois between Chicago and Saint Louis. Here, due to the high speed of the trains, gates that totally prevent road traffic from reaching the tracks are mandatory on all level crossings, and steel mesh nets are being tested on the busier crossings to further prevent collisions.

Safety

The original design for a level crossing consisted of a flagman in a nearby booth who would on the approach of a train, race out with a stop sign or red lantern and (attempt to) stop all traffic and clear the tracks. Manual or electrical closable gates which barricaded the roadway were later introduced. The gates were intended to be a complete barrier against intrusion of any road traffic onto the railway. With the appearance of motor vehicles, this barrier became less and less effective, and therefore pointless. Rising wage levels made the continuance of the older style crossing financially impossible. The decision was reached to substitute comparatively flimsy, but highly visible, unmanned barriers operated by the approach of a train but which are not linked with the railway signalling system, and to rely on road users following the associated warning signals to stop. In some cases the barrier only closes across the approach lane, and the other lane has no barrier. This is intended to allow slow vehicles to escape from a crossing when the barriers are dropping. It unfortunately allows impatient drivers to zig-zag round the half barriers to avoid any delay, and provides a potential collision risk.

In many countries, on less important roads and railway lines, level crossings are often "open" or "uncontrolled" but these have warning lights or bells to warn of approaching trains. Ungated crossings represent a safety issue; many accidents have occurred due to failure to notice or obey the warning. Railways in the United States are adding reflectors to the side of each train car to help prevent accidents at level crossings. In some countries, such as Ireland, instead of an open crossing there may be manually operated gates, which the motorist must open and close. These too have significant risks, as they are unsafe to use without possessing a knowledge of the train timetable: motorists may be instructed to telephone the railway signaller, but may not always do so.

The consensus in contemporary railway design is to avoid the use of level crossings. The director of rail safety at the UK Railway Inspectorate commented in 2004 that "the use of level crossings contributes the greatest potential for catastrophic risk on the railways." Eighteen people were killed in the UK on level crossings in the 2003-4 period. Bridges and tunnels are favoured, and there is a commitment on the part of UK rail authorities not to build new level crossings, and to reduce the number of existing level crossings from the present 8,200. The cost of making significant reductions, other than by simply closing the crossings, would be substantial, and a number of commentators argue that the money could be better spent. Some 6,500 of the 8,200 crossings are user-worked crossings or footpaths, with very low usage.

In November 2004 there were two major accidents on UK level crossings: one involved a car driver suspected of being a suicide, who caused the death of seven people (see Ufton Nervet rail crash); another involving a train carrying 50 school children resulted in no fatalities but a number of injuries. These incidents have increased efforts to review the placing of level crossings and to eliminate them where this is practicable. In the UK it has also been suggested that cameras similar to the type used to detect drivers who run traffic lights be deployed at level crossings, and that penalties for ignoring signals should be much more severe.

Third rail systems may also have level crossings: there is a gap in the third rail over the level crossing, but in spite of that the power supply is not interrupted since trains have current collectors in the front and rear cars; however, care must be taken that a current or voltage gap is not created between the two ends.

At railway stations a pedestrian level crossing is sometimes provided to allow passengers to reach other platforms in the absence of an underpass or bridge.