Design
The Burnley Tunnel is 3.4 kilometres (2.1 mi) long and comprises 460 metres (1,509 ft) of cut and cover at the west portal, 2.84 km (1.76 mi) of driven tunnel, and 180 m (591 ft) of cut and cover at the east portal. The gradient at the west end is 6.2% downhill for traffic, then relatively level until a 5.2% grade out of the tunnel. During construction a shaft located at the midpoint of the tunnel was used to speed up work, as it provided another two working faces for the roadheaders used. The shaft is today used for ventilation and emergency egress, in addition to a 1,420-metre (4,659 ft) long pedestrian tunnel that parallels the eastern part of the tunnel. Eight cross passages link the main and emergency tunnels, two more cross connects provide an emergency exit to the Domain Tunnel, and two emergency refuges are also located in the tunnel. Unlike the shallower and shorter Domain Tunnel, it passes deep under the Yarra River. It was subject to significant engineering problems and delays during construction due to unexpectedly high water pressures at its maximum depth of 65 m (213 ft).
A variable speed limit applies to traffic in the tunnel. In normal circumstances the speed limit is 80 km/h (50 mph), but a 40 km/h (25 mph) speed limit applies during maintenance. The speed limit during peak periods is often reduced to 60 km/h (37 mph) to prevent unnecessary congestion at the Monash Freeway. Regular radio transmissions can be received while in the tunnel because many radio stations have installed their own transmitters. Normal radio broadcasts can be interrupted by management announcements over all channels.
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