CO ROCKY MTNS Doubledeck low-vehicle lanes proposed

CO I-70 ROCKY MTNS

Doubledeck low-vehicle lanes proposed

A Denver engineering firm Jorgensen Hendrickson & Close Engineering (JHCE) has designed a relatively low-cost capacity enhancement for the congested I-70 tunnels through the Rocky Mountains between Denver and the ski resorts to the west. Ib Falk Jorgsensen of the JHCE engineering firm has designed a single lane suspended deck scheme for each of the present 2-lanes tube Eisenhower tunnels, increasing the overall laneage from 4 to 6-lanes.

Travel to and from the ski-fields from Denver has become a major source of aggravation and congestion is seen as a potential threat to the economy and way of life in the Rocky Mountains. With 30k veh/day on 4-lane I-70 and its long 5% grades, congestion is a major issue. Average speeds of 20 km/hr are common in peak travel times.

The option of widening the entire 160km route from 4-lanes to 6-lanes is estimated to cost $2.5b including $700m for a third 2-lane tube for the Eisenhower tunnel, which is located midway along the route at the continental divide. Selective widening and interchange improvements combined with time-variable tolls to move traffic onto the shoulders of the peaks might cost $900m and be self-financing. It seems likely to be recommened as a first stage solution.

Eisenhower Tnl enhancement is probably a second stage improvement.

Among those locals who attend public meetings and sit on citizen advisory groups there is a childish enthusiasm for various electric rail schemes but these are immensely expensive (over $4.0b) because of the long tunnels needed and steep grades and it is unclear that they would reduce demand for highway space significantly (people want cars at the resorts in the mountains.) The professionals working the Major Investment Study say major improvements in highway conditions are essential and are leaning toward a phased approach involving some tolls, since there is little prospect of substantial tax monies. Tolls have the additional advantage if varied of helping spread demand in time and of making more efficient use of expensive infrastructure.

The highest priorities are interchange improvements to reduce backups onto the mainline. These will likely utilize roundabout interchanges (already successfully installed at Vail) in place of diamonds and longer ramps. Extra climbing lanes on the steepest grades are needed immediately. Increasing capacity in the Eisenhower tunnel will eventually be needed, whatever else is done (see TRnl#22 Dec97 p7).

The suspended tunnel decking proposed by JHCE would be placed over the inside lanes of each tube, and would allow 2-lanes of low vehicles per tube. The outside lane allowing tall vehicles would be unaffected. Colorado DOT which is in charge of the major investment study in the corridor has included the suspended deck scheme in its list of options following the JHCE submission.

JHCE estimates the cost of the suspended decks at $70m vs $700m for construction of a new third 2-lane tube. The Eisenhower tunnel is 2.7km long and has generous cross-sections — tubes with a vehicle space 5.1m (16’8) high, and 8.8m (29’) wide. With the roadways marked to standard 3.6m (11’8) lanes, each lane would have a comfortable 0.4m (16”) spare space on either side of the edge markings. With a deck 0.3m (12”) thick, the height would provide for 2.4m (7’9) headroom in each of the low vehicle lanes, which accomodates most cars (1.3m to 1.4m high) but would be a tight fit for vans, larger pickups and sports utility vehicles which can be as high as 2.1m — especially with skis atop.

Headroom needs: Tunnels need to provide some (the French say 0.5m) clearance overhead for signage and lighting to be hung from the ceiling and a certain amount for psychological comfort — how much is debated.

Gary Alstot of Laguna Beach CA has proposed low-vehicle low-level doubledecking of sections of freeways in the LA area with the second decks going under overpasses. (TRnl#5 Apr96 p5) This contrasts strikingly with the high-level over-the-overpasses doubledecking roadway built by Caltrans for HOV vehicles over the median of the I-110 Harbor Fwy immediately south of downtown LA — a spectacularly high structure that most local communities would reject for its massive scale, shadowing and general intrusiveness.

New York area parkways such as the Sawmill built in the era of Robert Moses in the 1920s and 30s are the major existing example of low vehicle roadways in the US, and being free of large vehicles and designed by naturalistic landscapers are among the most pleasant roads to drive. Many of these are built with charming stone overbridges with only about 3m clearance. Moses said that politicians would cave in to the truck lobby if he did not build the parkways with low bridges to physically block truck movement.

The most ambitious low-vehicles project under way is the investor built doubledeck low vehicle tunnel which completes the missing link in the Paris A86 peripheral road in the Versailles area. 10km long this doubledecker tunnel will have 2.55m (8’4) ceilings. Entry will be restricted to vehicles under 2m (6’8), the 0.55m being left as minimal psychological headroom and space for hung signs. The vehicle lanes, 3 on each level, will be narrow, 2.9m (9’6), grades up to 5% and the posted speed limit will be 70 km/hr. Cofiroute, the toll company building the Versailles low-vehicle tunnel, estimates that 85% of vehicles in the Paris area are vehicles less than 2m height and company officials said it is far more economical to build for these than for all size vehicles. In a tunnel of the same bore as a 2-lane all-vehicles design accomodating the largest trucks it is possible to insert 2 decks of 3-lanes of low-vehicles, producing throughput of 5,700 veh/hr/direction compared to 1,400 veh/hr/dir, Cofiroute says. The company has a concession to build a shorter (7.5km) and more gently graded 2-lane all-vehicles tunnel (5m headroom) further west of the 2x3-lane low-vehicles Versailles tunnel, but this is far less attractive financially and there is no action on it scheduled (TRnl#6 Aug 96 p1).

A small fleet of special low emergency and service vehicles is being built for the A86 tunnel because regular firetrucks, towtrucks etc would not fit. This is slightly less of a problem in the single-lane doubledecking proposed for the Eisenhower Tnl since one full height lane will remain available for high emergency vehicles right alongside the doubledeck section.

Another possible application for the JHCE scheme would be on the Pennsylvania Turnpike which has five 2-tube/2-lane tunnels, four of these on the (I-76) east-west mainline (Blue Mountain, Kittattinny, Tuscarora, Allegheny) and the LeHigh on the NE Extension (I-476). All of these face overcrowding, but have traffic volumes rather neatly split about 1/3 heavy trucks 2/3 light vehicles which would make good sense of the 2 light vehicle/1 heavy veh configuration provided in the Eisenhower single lane suspended deck format.

The Eisenhower tunnel if it were built today would make use of in-tunnel jet fans for ventilation rather than the bulky longitudinal ducting and end-of-tunnel exhaust tower fans. Jet fans have the advantage of reducing the excavation needed, by 20 to 30% since they eliminate the ducts, and simply move air along the vehicle space. If JHCE’s ingenious scheme for hanging a deck in the existing vehicle space is not considered to provide enough headroom then a further option would be to demolish the longitudinal exhaust and supply ducts, using that space for the extra headroom for vehicles, gaining an extra 2m to 3m. Jet fans to move the fumes along the tunnel would need to be installed. Such a solution would add perhaps $25m to $40m to the cost of the JHCE scheme but would increase ceiling heights in the doubledeck side from the very low proposed 2.4m to 3m or more.

Cofiroute format: Another configuration could provide 8-travel lanes in the present two Eisenhower tubes, accomplished by replicating the Cofiroute scheme for Versailles. One tube would run heavy vehicles, a single lane each direction with no structural changes to that tube needed, but truck lane flyovers at each approach. The second tube reserved for low vehicles would be double-decked wall to wall — and striped for 3-lanes of 2.9m each on both decks. This truck-tube/car-tube scheme would provide the greatest vehicle throughput, and would have the virtue of completely segregating light vehicles from heavy trucks. It might be the cheapest method, in that work would be concentrated in one tube and the new deck would be a simple single span, with no hangers needed.

The JHCE single-lane doubledecking in each tube might provide more flexibility however. The single-lane second deck in each tunnel could readily be reversible, allowing 4-lanes westbound, 2-lanes eastbound Friday nights when the dominant traffic flow is up into the resorts, and the reverse Sunday nights. Narrower 2.9m lanes in the fully doubledeck low-vehicles tube could probably not be safely run contraflow.

JHCE has designed the single lane hung deck to be built of 900 precast concrete deck sections 5m x 3m supported on 300 9m long precast girders. The girders would be hung from 301 hangers going up through the supply duct area and anchored into the rock above. They say that the construction could be completed in 12 months. Tubes would need to be closed, one at a time between 10pm-6am for 18 weeks.

The transition to the doubledeck outside the tunnel portals would be accomplished with a third 2-lane approach roadway, splitting into a cantilivered, then a suspended deck inside precast frames that would span the existing lanes.

In Darlinghurst in central Sydney Australia work is underway on a 3-lanes atop 3-lanes all-vehicles tunnel (called Eastern Distributor) in which the deck consists of precast elements placed on rock benches. A single high tunnel doubledecked is cheaper than two single-level tunnels to construct and it simplifies interchanges at the ends, they say, compared to separate twin tubes. Also in a city it is threatening to fewer property owners above to concentrate the works along one alignment. (Contact Ib Falk Jorgensen JHCE 303 989 9000 JHCE@aol.com, Gary Alstot LA 714 376 1979 knoncent@ix.netcom.com, Philippe Garnier Cofiroute 33 1 41 14 7000, Dennis Eagar Leighton 61 2 9415 2509)