LBJ FWY DALLAS TX:6 HOT, 8 Free lanes plan Pans Out

At present the LBJ has 2x4 unrestricted lanes and a pair of concurrent flow HOV2Ls. It carries over 250k veh/day east-west across the north of the Dallas metro area with the Dallas-Ft Worth airport at the western end, traffic demand that is expected to rise to 400k veh/day. A long process of public consultation and consideration of alternates has chosen the 4-6HOT/8-free lane configuration as the consensus choice for a rebuild that will start in about 2001 and extend through 2015.

Present speeds in the AM peak are 53mph in the HOVLs and 45mph in the main lanes, while in the PM peak the difference is more striking – 46mph in the HOVLs vs 26mph in the main lanes

The I-635 corridor is being designed for a total of 132 lane-km of HOT lanes spread over 33km (20mi) of centerline route, divided 10km 6-lanes HOT (I-35E to TX-289), 13km 4-lanes HOT (just west of I-35E and TX-289 east to Plano Rd), 10km 2-lanes reversible HOT (Plano Rd to I-30.)

The prelim feasibility study says: “The rationale for recommending HOT lanes is that high occupancy vehicle (HOV) lanes would not be fully utilized... In order to optimize usage of these lanes, SOVs would be allowed to use the lanes as long as the total volume in the HOT lanes did not grow in excess of LOS C – meaning travel speeds remain at the highest levels. The mechanism to regulate the SOV traffic would be to implement high enough tolls so that the total number of HOVs and SOVs always provides traffic operations at or better than LOS C. Tolls will vary by time period and direction depending on the level of congestion in the main lanes.”

The report says HOT lanes:

(1) continue to provide a carpooling incentive

(2) use excess HOVL capacity and provide optimal lane usage in preak periods

(3) generate revenue

They could have added:

(4) provide the choice of premium service to SOVs on especially urgent trips

The planned HOTL system contains 32 on and off ramps.

Under the Dallas North Tollway there will be twin 3-lanes in mined tunnels. Two options are being examined:

• a pair of 4km long (13k ft) mined tunnels

• a shorter mined section and doubledeck/ trench/cantilever combinations

Longest tunnel in US

Under a head “Out of sight, Out of Mind” the latest LBJ CIRCULAR reports: “Depressing the HOT lanes will permit (them) to be built with minimal right-of-way impacts, and the noise and visual impacts to the adjacent properties will be virtually non-existent... (T)hrough the LBJ/Dallas North Tollway (DNT) interchange, the HOT lanes will have to be lowered and covered to minimize impacts to the surface roadways and pass underneath some major drainage crossings. Two options continue to be studied in this area. The first involves extending the standard design of placing the HOT lanes underneath the frontage roads for as long as possible and utilizing a cut-n-cover design or very short tunnel section in the immediate vicinity of the LBJ/DNT interchange. The other alternative is to construct two longer tunnels from Midway Rd to Preston Rd. Each tunnel will carry three HOT lanes for a distance of approx two miles (a draft design is 3960m, 2.46mi – TRnl). The tunnels would be the longest and widest automobile tunnels in the country.”

Dallas geology is perfect for tunneling – a stable, easily mined limestone. Considerable experience has been gained tunneling in the area with a rail transit system and the Addison airport tunnel. The tunneling needed here would be 24 lane-km for $170m, an estd cost of $7.1m/lane-km ($11.3m/lane-mi).

That involves excavation of a horseshoe section approximately 15.2m wide (50') and 8.8m high (29'), providing 3x 3.65m lanes (12') and 0.5m offset and a 0.9m wallkway each side. Clearance would be a minimum 5m (16’6) allowing space above for ventilation jetfans and signs but the top of the ceiling would be over 8m (26'). An option would be enlarge the tunnel by about another 3m width to provide a full breakdown shoulder in each tunnel, which would add about 20% or $35m to the cost.

Overall cost of the total project over 33km (21mi) is estimated at $1200m, including $182m for the LBJ/US-75 IC which is often regarded as a separate project and is already beginning construction. Final design has begun on the rest of the project with the aim of construction beginning in 2002 and will continue over at least 10 years.

The long mined tunnels are competitive with the cost of structure once property acquisition, legal expenses and traffic maintenance are taken into account. They represent the most straightforward kind of construction under traffic and can be built entirely within the existing right of way. These would be the longest highway tunnels in the US, but much shorter than a bunch of road tunnels in Japan and Europe. The Burnley tunnel on Melbourne’s CityLink is the most similar in scale. It is 3-lanes and 3.4km though it was built through far more difficult geology.

The feasibility study of HOT lanes operations involved a multi-staged assignment process (see below). WSA assumed that the HOT lanes would be priced to allow 65mph travel at all times and a threshold of 1800 veh/lane/hr was assumed to be about the limit for free flow traffic. The modeling suggested the best strategy for a complex multi-entry/exit HOT lanes system will be a minimum toll in the peak hour peak direction of $1.20 and 20c/mile. Off-peak 10c/mi could be collected with no minimum toll. The HOT lanes will have time savings at all times of the day.

Toll revenue would be $42k/average weekday split between AM peak $11k, PM peak $19k, midday off-peak $11k, night $1k for an annual $12m. That is based on estimated time savings eastbound of 10mins AM peak, 6mins PM peak, 4mins midday offpeak, 2mins nights. And westbound time savings are 7mins, 9mins, 7mins and 3mins. The 65mph speed of the HOT lanes gives a journey time of 18 to 19mins. (The PM peak earns more revenue than the AM peak in part because it lasts 4hrs vs 3hrs for the AM peak.)

The modeling was based on average conditions and produced average optimal tolls in part to estimate toll revenue potential, but the report comments that in practice the facility managers would probably be best to implement dynamic pricing responsive to traffic conditions day by day, as on I-15 in San Diego. WSA modeled solely for private cars assuming all trucks ere excluded from the HOT lanes. They comment that small package delivery vans and other agile commercial vehicles might well be allowed on the HOT lanes. That would enhance the revenue potential of the facility. (See TRnl#16 Jun 97 p1, TRnl#36 Feb 99 p13, Contact Matt MacGregor 972 437 0101 MMACGRE@mailgw.dot.state.tx.us)