Here is detailed information about road closures for the Cardiff 10K:

Saturday 1st September at 0800 to Sunday 2nd Sept 1800:
City Hall Road, Corbett Road, College Road, King Edward VII Avenue, Museum Avenue and Gorsedd Gardens.
Access / egress to Queen Anne Square & cyclists maintained.

Sunday 2nd September 2018
The following roads, traffic lanes will be closed on from 08:45 to 12:45 hours, with cordon controls excepting (i)below, at the outer closure points, at:
(i) The A48 Western Avenue nearside westbound lane from the Taff River Bridge to its junction with Mill Lane.
(ii) North Road across its junction with Corbett Road/North Road.
(iii) Castle Street, Westgate Street north of its junction with Park Street, Duke Street, Kingsway south of Friary Gardens, North Road south of Colum Road, Boulevard de Nantes, Museum Avenue and Gorsedd Gardens Road.

The following roads, traffic lanes will be closed from 08:45 to 11:15 hours, with cordon controls at the outer closure points, at:
(i) Westgate Street, Wood Street, Fitzhamon Embankment, Despenser Street, Cowbridge Road East east of its junction with Neville Street, Lower Cathedral Road north of its junction with Neville Street.
(ii) Penhill (except for access), and Cathedral Road.

Cathedral Road will be closed in both directions with marshals at each junction. Care will be taken to try to minimise disruption and, when there are gaps in the stream of runners, where possible to allow vehicles to cross Cathedral Road, this will be undertaken by marshalls but only where safe to do so.