It is one of the ten international equestrian sport horse disciplines recognized by the Fédération Équestre Internationale (FEI).

[3] Grooms are required for safety reasons because the driver must stay on the carriage at all times, holding the reins and controlling the horses.

Most marathon carriages are of a modern design, built from steel or aluminum, with hydraulic disc brakes, a low centre of gravity, and a very small turning radius.

All carriages for the marathon phase are 125 cm minimum track width, measured on the ground and on the rear wheels.

The test is performed in a 40 by 80 or 40 by 100 metre arena with letter markers, where transitions in speed and gait are to take place.

At the lower levels, only one judge will normally be positioned at C (the centre of the short side of the arena) and the Test may have 16 movements.

Multiple horses are judged on ability to move in harmony and ideally will have similar conformation, action, and movement.

Horses are to remain on the bit throughout the test, maintaining impulsion, elasticity, rhythm, and forward movement.

It tests the fitness and stamina of the horses, as well as the driver's knowledge of pace, over a 10–22 km course, divided into 3 or 5 sections.

It has obstacles or "hazards" throughout the course to test the speed and agility of the horses, and the driving ability of the whip.

The groom also helps to keep the correct pace by checking the kilometer markers on the course against calculated timings for each section, allowing for ground conditions and the horse's fitness.

At club events, the rules may often be relaxed somewhat with, for instance, a "short marathon" which usually means only section E and (some of) the obstacles are driven.

Marathon obstacles, sometimes known as hazards, frequently take advantage of natural features, being sited around trees and on slopes, but are typically solidly-built sections of posts and rails.

Driving any horse or pony and carriage around an obstacle at speed requires practice and a rapport between driver, animal(s) and groom(s).

In all phases of the competition, a number of other infringements may also incur penalties, for example the driver or groom dismounting the vehicle, breaking of pace where a certain pace is prescribed, not carrying a whip in the dressage or cones, errors of course in the dressage, marathon obstacles or cones.

Some competitions (usually not international) may use other arrangements, for example: At National and Club level, further division is made according to the ability and experience of the driver.

In the UK, where the sport is known as Horse Driving Trials,[5] the levels of progression from Club to National competition are: Pre-novice, Novice, Intermediate, Open, and Advanced.

In New Zealand the sport is known as Combined Driving Trials,(CDT) [6] and the levels of competition are: Novice, Intermediate, and Open.

In 1998 a group of enthusiasts in Sussex, England, started a series of winter one-day competitions, based on the three phases of driving trials, but modified to take place in an indoor arena.

Completing the course too fast or too slow means the competitor is assessed penalty points for each second over or under the optimum time.

After the cones phase, two obstacles are built in the arena and the drivers and grooms walk them, choosing the best route for their turnout.

The drivers come back into the arena one-at-a-time in their class, in reverse order of their score placing – best goes last – and drive the two obstacles as fast as possible.

Although they were originally thought to be the poor relation of driving trials, indoor events are bringing more people into the sport – over 2,500 entries in 2012-13 – and provide a training ground for more serious competitors and their inexperienced horses and ponies.

These take place at venues throughout Europe, alongside other World Cup competitions, during the months of October to March.

[7] At his prior win, the final qualifier in Leipzig, Germany the announcer declared him "number one in the world, more titles than any other driver in history.

An international event must be organised under FEI Statutes, General Regulations and Sport Rules, and may be open to competitors of all national federations.

In addition, a World Combined Pony Championships (CH-M-AP, which include singles, pairs and four-in-hand) are held every odd-numbered year.

[32] World Cup Driving events are classified as CAI-W and take place throughout the winter months (Nov to April).

Competitions for drivers with disabilities are classified as CPEAI (Paralympic Equestrian) and the championships (CH-M-PE-A) are held in every odd-numbered year.

Keen drivers can qualify to take part in national events from which they may put themselves forward to be selected to represent their country at international competitions or World Championships.