Dozens of foreign diplomats are regularly caught breaking a specific road rule in the nation's capital.

In the past 18 months, police have caught 76 diplomats running red light arrows, the latest Justice and Community Safety Directorate figures show.

The diplomats drove their vehicles - often marked with easy-to-spot ''DC'' or ''DX'' prefixed number plates - into intersections or onto crossings while the arrows were still red, thereby ignoring a clear signal to stop.

It was one of the most common traffic offences by diplomats, who represent more than 90 nations and inhabit some of the most expensive properties in the ACT in suburbs such as Yarralumla and O'Malley.

The most common infringement was speeding. But the majority of diplomats did this in the safest way possible with 685 caught in non-school zones driving at less than 15km/hr above the limit, the most minor speeding offence there is.

This sort of driving incurs a $203 fine and one demerit point while ignoring a red-light arrow attracts a $340 fine and three demerit points, but it appears many of these fines will not be paid.

Almost 40 per cent of traffic fines given to foreign diplomats in Canberra have so far not been paid in the 18 months to February.

Diplomats have racked up 340 unpaid traffic fines since August 2012, while 550 fines have been paid in the same period.

All up, the 890 infringements, which did not include drink driving, driving dangerously or parking fines, incurred $303,885 in penalties.

''Diplomatic missions do not disclose specifically that they are relying on diplomatic immunity,'' a directorate spokeswoman said.

In the same period across the general ACT population, but excluding diplomats, there were 113,111 traffic and camera infringements worth $28 million.

So far there were 6371 infringements not paid, although those incurred last month were not yet due.

Diplomats appear to pay a higher ratio of parking fines.

In the past 18 months, just 263 of 731 parking fines have not been paid so far, or about $37,000 worth.