Passing beneath Lawrence and back over the East Don River, the expressway begins climbing out of the valley once more. It reaches the top of the valley and curves along a plateau before passing over York Mills Road. Residential sub-divisions are present along both sides of the road, isolated from the expressway by noise barriers, from north of Lawrence to the Highway 401 interchange. After rising to meet the interchange, it widens to four lanes and splits into two branches: two lanes continuing north as Highway 404, and the three others as Highway 401. The entire length of the parkway uses the RESCU Traffic Management System, which was installed in 1994. Like the similar COMPASS system on provincial freeways, RESCU combines in-pavement sensors with traffic cameras and changeable message signs (6 fixed and 10 portable) to alert drivers of accidents, traffic conditions and upcoming closures. The system is used as a means of managing traffic flow along the parkway. The message signs also frequently display non-urgent messages to motorists, such as notices for future construction, safety messages and smog alerts. The RESCU Traffic Cameras are located at regular intervals along the parkway. The cameras, which are operated by the City of Toronto, can be viewed on television and online. The cameras are located on poles and are fixed in direction. There are 16 camera locations on the parkway. Most have one camera for northbound and one for southbound traffic. RESCU operators monitor the cameras for emergency purposes; local radio and television media use the service for traffic reports. The Don Valley Parkway, along with the Gardiner Expressway, is one of Toronto's busiest municipal routes. It is the sole north–south expressway into Toronto's downtown, a role it was not designed to support. The parkway was planned as one of a series of expressways to provide commuter routes to downtown from the expanding suburbs. Two other un-built expressways were planned: the Scarborough Expressway, expected to handle traffic between downtown and the eastern suburbs, and the Spadina Expressway, expected to serve traffic from the north-west. By the early 1980s, traffic volumes on the parkway exceeded capacity, and today, the parkway has significant traffic congestion on most days. During the morning commute, commuters fill the southbound lanes as far south as Bloor Street. In the afternoon/evening commute, commuters fill the northbound lanes from Bloor Street, and often the full length of the highway in event of a collision or other hazard.