The A873 is a short rural A-road in south Perthshire, part of the Trossachs Trail. Originally numbered B825, it was given its current number in the mid-1920s.
For many people, the A873 starts at a fork junction on the A84 near Blair Drummond Safari Park, a couple of miles south of Doune. Heading from Stirling, traffic barely has to slow to fork left at the junction, which utilises a short section of the old A84 line. Heading west, the road winds through fields, passing the junction with the B8031 before straightening up for a mile-long straight. A few bends later, the road approaches Thornhill, the only settlement of any size along the route. The long main street reaches a crossroads in the middle of the village, where the A873 swings sharp right past a clock tower, with the B822 joining from the south. After a brief multiplex, the A873 turns westwards once more, with the B822 continuing to the north.
Leaving Thornhill behind, the road winds through fields, and despite a couple of minor realignments, it is never as straight as the eastern section. It is climbing too, offering some good views south across Flanders Moss and the River Forth to the Campsie Fells beyond. The tiny village of Blairhoyle has a couple of sharper bends, but the road is nearly at its end, soon reaching the A81 at a TOTSO, the mainline continuing ahead towards Aberfoyle. This then is the quickest route from the Motorway network into the heart of the Trossachs, and as such the road can be clogged with coaches. East of Thornhill, the width and alignment mean that there are few problems, and good overtaking opportunities, but be prepared for slower progress the further west you get!