HOUSTON I-45 Parkway + Tunnel

Houston I-45 Parkway & Tunnel Concept

TxDOT's original reconstruction of I-45 extended from I-10 north of downtown to The Woodlands, about 30 miles. The proposed tunnel system will extend from US-59 south of downtown to Beltway 8 at Greenspoint, about 14.5 miles.

The benefits of constructing roadway tunnels using tunnel boring machines include:

  • Limited impact to existing roadways.
  • Limited traffic delays.
  • Accelerated construction - Less than 4 years.
  • Maintains existing capacity during construction.
  • Decreases construction and traffic conflicts.
  • Minimal environmental impact.
  • Avoids change orders.
  • Design, build and finance.


The proposed parkway & tunnel concept consists of:

  • Two large diameter tunnels with six traffic lanes per tunnel. One tunnel for each direction. These roadway tunnels are to be toll only facilities.
  • Relocation of existing HOV traffic into the tunnels allows to implement high capacity transit rail to be place in the center of I-45 extending from Pierce Elevated to Greenspoint Mall.
  • Eventually the existing I-45 main lanes can be reconstructed into a system of limited access express streets similar to Allen Parkway and service roads reconstructed into boulevards. This would enhance ridership of rail located in the middle of the corridor and development of transit oriented development.
  • In case of hurricane evacuation the twin tunnels can be used as emergency shelters housing over one quarter of a million people.

Tunnel Boring Machine Technology Allows Construction of Roadway Tunnels Without Disturbing Existing Traffic

Picture on left shows a tunnel boring machine (TBM). TBM can actually bore the roadway tunnel under the existing I-45 without disturbing existing traffic since all work is done below ground. The simplicity of boring and construction of tunnels makes this process very efficient and faster than reconstructing highways at grade shifting traffic from the old to new lanes and using temporary lanes.

New TBM technology makes roadway tunnels to be price competitive with other types of highways such as at-grade or elevated highways in particular when located in urban areas.

Tunnels Are Designed Not To Flood
Storm Allison (US-59)
Storm Allison (I-45)
Storm Allison (I-10)
It is to be expected that some roadways in Houston flood during heavy rains, including some highways. Tunnels are built underground and designed for ground water not to penetrate into the tunnel. Tunnels are protected from weather conditions including: floods, heavy rains, hurricanes, heat, and provide drivers a dry and safer driving environment than the normal at-grade highways that are affected by weather conditions.
Map shows emergency evacuation routes. I-10 and I-45 are part of the emergency evacuation route. Note pictures above - these highways are not accessible when flooded.


How Are Tunnels Designed Not To Flood
Picture on left shows how the entry or portal to a tunnel is designed in such a way that water does not flow into the tunnel. The design establishes the entry road to be at a level higher than the expected water elevations. This prevents surface water to flow into the tunnel.
Above rendering shows how elevating the roadway before entering into the tunnel prevents flood waters from entering the tunnel. Also it is possible to provide a gate at the tunnel portal to close the tunnel and thus preventing any water entering the tunnel.
Roadway Tunnels Purify Air Pollution and Prevent Noise Pollution

The most common highway design is at-grade where the highway and service roads are about the same elevation of adjacent properties.

Unless sound walls, trees or other element is installed along the highway, this type of roadway design provides no mitigation for air pollution and noise pollution.

Some highways are built below grade in a trench. In Houston US-59 between downtown and the Galleria was designed below grade.

Although this type of design provides some mitigation for noise pollution the below grade segment of US-59 does include sound walls to further noise mitigation. It also offers some mitigation for air pollution but ultimately air pollutants are not mitigated.

Elevated highways is another design alternative. Although this type of design may reduce horizontal expansion of highways it creates other problems. Because it is at a higher elevation noise and air pollution is propagated to greater distances.

Elevated highways also tend to collect more trash and debris under the structures and are a type of visual pollution.

Roadway tunnels are the least obtrusive type of highway design. First, tunnels enclose vehicular emissions and through its ventilation system allow the application of air purification allowing to filter air particles and toxins before air from the tunnel is ventilated outside. Second, tunnels eliminate noise pollution generated by vehicles.

In many cities roadway tunnels are being constructed as an alternative to expand highways and to eliminate them from the surface. Corridors that used to be occupied by these highways are now developed in green spaces open to the public. With added vegetation and outdoor activities these green corridors enhance the quality of life.

Roadway Tunnel Safety

Safety is an integral part of tunnel design. Unlike other types of roadway design, the design of roadway tunnels has to take in consideration many aspects of traffic operations and safety.

Generally the design of roadway tunnels include, among others: ventilation systems, emergency exits, standpipe systems, tunnel surveillance, vehicle guidance, and emergency evacuation plans.

Because roadway tunnels are generally one-way and have limited access, these type of facilities are more efficient in conducting traffic and reduce potential conflicts for crashes. In addition, because roadway tunnels are protected from the weather, weather conditions do not have a negative effect on traffic flow in roadway tunnels.

Most roadway tunnels include surveillance systems which allow implementation of emergency strategies in an efficient and expeditious manner.

Intelligence transportation systems (ITS) are an integral element in the operation of roadway tunnels. Real-time information, changeable message signs, and emergency evacuation are some of the ITS applications included in roadway tunnels.

Although emergency evacuation is incorporated in the design of roadway tunnels, tunnels also include: safety changers, safety shafts, and cross passages.

Cross passages connect the roadway tunnel to an adjacent tunnel or to an alternative safety/access shaft. This provides for an alternative emergency evacuation route for people and/or vehicles. The picture on the left shows the cross passages in yellow.

Cross passages can be designed in a manner that could allow roadway tunnels to become "reversible" lanes. This particular need was demonstrated in Houston during the hurricane Rita evacuation when some highways were transformed to reversible lanes.

In many European countries roadway tunnels are designed with the additional purpose to provide emergency shelter. This is a unique characteristic the only roadway tunnels can provide. In case of urban areas such as Houston that are hurricane prone, roadway tunnels can be designed for hurricane emergency shelters thus providing shelter not for people only but also for emergency vehicles that could be needed in the aftermath of a hurricane.

Roadway Tunnel "Hurricane Emergency Evacuation/Shelters"
Houston cannot afford not to have a roadway system designed for emergency evacuations.

Picture of traffic evacuation prior to hurricane Katrina

Picture of traffic evacuation prior to hurricane Rita

In developing the alternative design of roadway tunnels for the I-45 corridor it was necessary to pay careful attention to emergency evacuation since I-45 is a designated emergency evacuation route. Early in the process it was obvious that for an emergency evacuation event it would be necessary to control the entries and exits to and from I-45. This was proven to be a significant factor during the Rita evacuation.

Roadway tunnels in effect provide for a more superior design and infrastructure during emergency evacuations because: provide for limited access, protect drivers from weather conditions, limit the need of shifting lanes, provide real time messages, and ultimately can provide emergency shelter.

Roadway Tunnels - Time Value Savings
Time and method of construction has a significant effect in the cost and development of roadway construction
As roadway projects become larger and takes longer to construct it is important to understand the time value of the project. For example, per TxDOT's 2005 cost estimates of the I-45 preferred alternative, the 33-mile roadway reconstruction would take 14 years and cost an estimated US$2.1 Billion.
Assuming that: design would take 4 years, construction would take 10 years, the cost of design is 10% of the total cost, and disbursements of funds for construction are of equal 10 annual payments.
The final cost of the project based on the 2005 estimate of US$2.1 Billion using F = P (1+i) ^n for i of 10%, 15% and 20% are shown below. These values are much greater than the estimated 2005 cost of the project.
i F
US$ 5.12 Billion
US$ 8.02 Billion
US$ 12.55 Billion
A 15% increase per year is very possible, in fact last years construction costs have increase in the range of 20% per year. Thus at a 15% increase of construction cost per year the calculated cost of the project is SU$8.02 Billion
This "future" value of the project has to be considered when looking at alternatives for reconstructing I-45.
One of the unique characteristics in the construction of roadway tunnels is the short time required for building them. For example a high speed 33-mile long railroad tunnel in Europe was recently constructed in 28 months. Of course adding TBMs could decrease the time of construction significantly.
Other unique benefits in the construction of roadway tunnels is the limited impact on existing traffic, businesses, and residents.
Some basic cost estimates for a six-lane 50-foot diameter roadway tunnel set it at about $160 Million per mile. Based on this cost estimate the proposed 15 miles of I-45, from US-59 south of downtown to Beltway 8 at Greenspoint, would cost about US$4.5 Billion which is cost competitive to the preferred alternative identified by TxDOT.