John M.W. Aldridge: I-70 ‘hard shoulder’ solution most promising | SummitDaily.com
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John M.W. Aldridge: I-70 ‘hard shoulder’ solution most promising

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Since last September’s release of the Colorado Department of Transportation’s decades-away $20 billion train plan to fix capacity and congestion problems in the I-70 mountain corridor, it is gratifying to hear that short-term and affordable alternatives are under consideration. The “zipper lane” and “hard shoulder” concepts can resolve the heart of the congestion problem and provide many years of relief for all travelers, including trucks.

The heart of the congestion problem is the 15-mile stretch from Floyd Hill to Empire Junction. Currently in the westbound direction, congestion begins at the top of Floyd Hill where a lane drop reduces the lanes from three to two. In the eastbound direction, congestion begins at the Eisenhower/Johnson Memorial Tunnels and then it increases hugely by the merge of traffic from US-40 at Empire Junction.

The “zipper-lane” concept would change the direction of a westbound lane to eastbound by means of a moveable barrier. The concept has significant problems, though. For instance, its deployment is limited to winter Sunday afternoons (when westbound travel is minimal). Therefore, congestion would still be severe coming home on a summer weekend. Moreover, the barriers can only be moved when there’s no or little snow on the roads, according to a CDOT study. If the zipper lanes were available this season, they probably would not have been deployable during the recent winter storms.



The hard shoulder concept is far more promising. It converts the shoulder to a travel lane, thereby increasing the number of lanes from two to three per direction. Presumably, (yet to be determined) the third lane would be open only during congested times and actively managed according to a set of operational strategies. The lane could be set up to respond to changing conditions via video surveillance and electronic signing.

Although a simple concept, hard shoulders would require some roadway reconstruction, a third bore at the twin tunnels east of Idaho Springs, and ramp modifications at interchanges.



Use of shoulders as travel lanes is not new. There are several examples throughout the U.S. and Europe. Most are used only during congested times, some are bus-only, and others are tolled and priced according to the degree of congestion. A November 2010 Federal Highway Administration Report to Congress, “Efficient Use of Highway Capacity Summary,” concludes that hard shoulders have proven effective and shown positive benefits.

A hard shoulder lane is relatively inexpensive and can be constructed within a short time. Construction can be segmented and kept off the main travel lanes – a significant advantage that would keep traffic moving during construction. On I-70, the eastbound lane from Empire Junction to the bottom of Floyd Hill would be first. The change includes a third bore at the Twin Tunnels east of Idaho Springs. During the lane’s construction, though, it may be possible to use the old highway on the toe of the slope as the shoulder lane. Second would be the westbound direction. In addition, hard shoulders could be deployed in other sections of the corridor – most notably on the uphill section of Georgetown Hill.

The shoulder lanes can be augmented with variable speed limits and/or limited to slow-moving vehicles. Areas for breakdowns could be added where there is room. Safety and incident management are of paramount importance to the public and CDOT. This is an area where CDOT can excel with active management (i.e., video surveillance) and stand-by emergency vehicles when the lanes are open to traffic.

Hard shoulder lanes are generally considered an interim solution. That’s particularly applicable here as it sustains the corridor stakeholder’s 35- and 50-year vision of an advanced guideway system. The hard shoulder lanes provide an eventual “platform” that could be converted to a guideway (piers or track), or could be used for an “on-alignment” high-speed rail system as suggested by the Rocky Mountain Rail Authority.

However, with increasing traffic, travelers can’t wait for a train that probably will never come. Now is the time to make efficient use of what we have and make affordable and sustainable improvements. Hard shoulder lanes fit the bill, perfectly.

John Aldridge is a professional traffic operations engineer and research associate in transportation policy at the Independence Institute. http://www.i2i.org


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