Design and Engineering
The present Lucan bridge, constructed in 1813 and designed by George Knowles, consists of a single span of 34m and a rise of 6.7m. The inspiration for Lucan came from Island Bridge (span 32m, rise 6.58m) but there is a significant structural difference in that, the former is a segmental arch while the latter, possibly oval.
The ashlar masonry on Lucan Bridge is superb and the see-through iron balustrade parapets and unobtrusive spandrels give it an elegant overall appearance from the river. The skewback, resting on an impost, is formed of three stones, with a springing face at 45 degrees to the horizontal. This is unusual for such a large arch; however the springings are backed each side by solid 1.83m thick pier abutments up to road level. The springing also commences less than a metre above rock level so horizontal movement is restricted.
Following the construction of the bridge the gradients and the vertical visibility were considered unacceptable so the approach roads were raised. Lucan Bridge is the one of the finest masonry arch bridges in Ireland and it is currently the longest such span in the country.