Almost 20,000 runners are tackling the 2016 SSE Airtricity Dublin City Marathon after having to contend with the unexpected obstacle of an unattended motorbike left at the start of the race.
In an apparent lapse in security, a blue BMW motorbike was left parked and unattended in the middle of the road just beyond the start of the race at Fitzwilliam Street.
Runners were forced to avoid the motorbike once the race began before the vehicle was cordoned off by stewards.
The incident will be of concern to race organisers as the bike, which had a tank bag on board, posed a serious obstacle during the most congested part of the course.
The entry of 19,500 makes this the biggest SSE Airtricity Dublin Marathon to-date.
The race was won by Ethiopian Dereje Debele Tulu while Namibian athlete Helalia Johannes was the first woman to cross the finish line.
The weather forecast calls for nearly ideal running conditions of mostly cloudy with a few bright or sunny spells. Overall it will be mostly dry but some patchy light rain or drizzle might occur at times. Met Éireann is predicting a light to moderate southerly breeze.
After beginning Fitzwilliam Street shortly before 9am, the route will wind on to the Liffey quays and through Phoenix Park before reaching Terenure and UCD.
The finish-line is at Merrion Square.
There are staggered start times for entrants due to the large number of participants. Runners will start according to their allocated Times Zone to ensure that there is less congestion in the early part of the race.
The wave system blends participants in mutually competitive groupings. There are 4 wave starts. 1st wave sub three hours and 35 minutes, the 2nd wave 3.35 to 4.05, the third wave aiming for 4.05 to 4.35, the final fourth wave of 4:35 plus.
The first to set off were wheelchair entrants at 8.55am. They were followed by the first wave of entrants at 9am. The 2nd wave departed at at 9.10am, the 3rd wave will set off at 9.20a followed by the final wave at 9.30am.
There are traffic restrictions and changes to Dublin Bus routes across much of Dublin this morning although these are expected to lift during the early afternoon as runners pass along the course. Dublin Bus routes 13, 16, 25, 46a and 69 are among a raft of services that will be affected over the course of Sunday.
Luas services are operating as normal.
Dublin Bikes stands on Merrion Square, Mount Street and Fitzwilliam Square will be inaccessible to 10am on Monday to facilitate preparations for the marathon.