How to Build a Road

- Building a mountain highway begins with finding a route that meets strict slope requirements. Roads must remain relatively level both along the direction of travel and across their width, even when the surrounding terrain is steep and irregular.

- Highway curves are deliberately banked to reduce the risk of vehicles skidding. Engineers calculate the appropriate banking, or superelevation, using factors including design speed and the radius of a turn.

- The Federal Highway Administration provides a formula for calculating recommended banking angles, but engineers disagree about the ideal approach. Some advocate greater banking to accommodate trucks with higher centers of gravity, while others warn that steep banking creates problems for slow-moving vehicles and icy conditions.

- Road banking generally does not exceed approximately 12%. Most curves use substantially less, and banking is concentrated on turns rather than straight sections.

- Highways generally aim to keep longitudinal gradients at or below 6%. This means a road rises or falls no more than approximately six units vertically for every 100 units horizontally, partly to allow heavily loaded trucks to climb safely.

- Interstate 70 was originally intended to end in Denver rather than cross Colorado's Rocky Mountains. Federal highway planners initially regarded a transmountain interstate through the region as too difficult to build.

- Intense lobbying persuaded Washington to extend I-70 across the mountains. The decision created the engineering challenge of finding a practical interstate route through exceptionally high and steep terrain.

- The E. Lionel Pavlo engineering company was tasked with identifying the cheapest and flattest mountain crossing. After approximately one year of work, it presented seven potential alignments.

- Following river valleys was one of the most promising methods for reducing mountain highway construction costs. Rivers generally follow valleys with relatively gentle downhill gradients, allowing engineers to avoid the enormous earthmoving costs of forcing a road directly over steep terrain.

- Correcting a road's longitudinal gradient is generally more expensive than correcting its sideways gradient. Cutting a level shelf into a mountainside is expensive, but flattening a long uphill route can require moving substantially greater volumes of earth across much longer distances.

- An estimated 50% hillside slope can double construction costs. Steep cross-slopes increase the amount of excavation and filling required to establish a sufficiently wide and level roadbed.

- The Colorado River demonstrates why river valleys are useful highway corridors. The narration states that the river loses approximately one mile of elevation across roughly 280 miles through Colorado, despite passing through mountainous terrain where nearby slopes can climb a mile vertically within a mile horizontally.

- The northern I-70 proposal was relatively inexpensive per mile because it followed the Fraser and Colorado Rivers. Its main engineering obstacle was crossing the Continental Divide, which would require a tunnel before the route could descend through the river valleys.

- The northern alignment was rejected partly because it passed through sparsely populated areas. It would have served fewer Colorado communities directly, reducing its usefulness to residents even though it offered comparatively favorable construction conditions.

- The southern alignment was estimated to cost approximately $55 million less overall than the northern alternative. Although it required crossing two high mountain passes rather than one, its shorter and more direct route outweighed the northern proposal's lower construction cost per mile.

- The Continental Divide presented an unavoidable obstacle because river valleys do not provide a continuous passage across it. Rivers on opposite sides drain toward different ocean systems, leaving high mountain ridges between otherwise useful valley corridors.

- Engineers considered building a road climbing nearly 12,000 feet or constructing a tunnel at approximately 11,000 feet to cross the Continental Divide. The road option would have required extraordinarily difficult gradients and mountain construction.

- The tunnel was selected as the more practical Continental Divide crossing. Despite requiring construction at approximately 11,000 feet, or 3,400 meters, the tunnel offered a more manageable solution to the region's steep terrain and severe weather.

- A second major routing problem existed between Silverthorne and Vail. Engineers initially proposed a direct alignment climbing a valley and passing through a tunnel beneath Red Buffalo Pass.

- The Red Buffalo Pass proposal would have preserved a shorter, more direct interstate alignment. Its disadvantage was the need for another difficult high-elevation tunnel through sensitive mountain terrain.

- The proposed Red Buffalo Pass alignment crossed the Forest Service's Eagles Nest Wilderness Area. Environmental opponents argued that allowing a major interstate through one of the country's highest categories of protected land was unacceptable.

- Growing environmental opposition changed the interstate's proposed route after planning had already begun. The controversy reflected increasing public resistance to major construction projects in protected natural areas.

- Agriculture Secretary Orville Freeman rejected the Red Buffalo Pass alignment. Because the Forest Service fell under his authority, Freeman had the final decision and required highway planners to find another crossing.

- Vail Pass became the alternative to Red Buffalo Pass. At approximately 10,600 feet, or 3,200 meters, it offered comparatively manageable gradients and could be crossed without constructing another tunnel.

- Choosing Vail Pass added approximately 10 miles, or 16 kilometers, to the highway. Engineers estimated that the detour would increase fuel and vehicle maintenance costs by approximately 94 cents per driver, but it avoided the protected wilderness and another major tunnel.

- The Vail Pass alignment combined manageable average gradients with difficult individual sections. Its average longitudinal gradient was approximately 4.5%, although the climb from Vail included sections exceeding the preferred 6% maximum.

- Creating a sufficiently wide roadbed across Vail Pass was a greater problem than managing its overall climbing gradient. The irregular mountainsides required extensive excavation, filling, bridges, retaining structures, and other specialized construction techniques.

- Highway construction begins with surveying and creating cross-sectional profiles of the proposed route. Engineers use these profiles to determine where the terrain must be cut away or filled to produce the required roadway width and elevation.

- Earthmoving calculations are commonly divided into 100-foot, or approximately 30-meter, stations. Engineers evaluate each station, sometimes including half-stations, to estimate the quantity of material that must be excavated or added.

- On hillsides, excavated material from the uphill side can be used to fill the downhill side. This cut-and-fill method creates a level road platform while reducing the need to transport material from elsewhere.

- On relatively flat terrain, highway beds are often raised above their surroundings. The additional fill allows rainwater to drain away from the road rather than accumulate on the pavement.

- Station-by-station earthmoving estimates help determine construction schedules, material requirements, and costs. Adding these calculations across an entire alignment provides an estimate of how much land must be physically reshaped.

- Earthmoving alone can account for almost a quarter of ordinary rural highway construction costs. A Florida Department of Transportation estimating model placed excavation and embankment costs for a four-lane divided rural highway at more than $1 million per mile.

- Colorado's mountainous terrain makes earthmoving substantially more expensive than in relatively flat regions such as Florida. Hard rock, steep slopes, and complicated geography increase excavation requirements and construction difficulty.

- Before I-70 crossed Vail Pass, motorists used U.S. Highway 6. This narrow, two-lane road followed the northern side of the canyon and was notorious for sharp turns and difficult driving.

- Some drivers avoided U.S. Highway 6 by taking the considerably longer U.S. Highway 40. The alternative offered a smoother and safer journey, illustrating the transportation problems the interstate was intended to solve.

- The new interstate needed to accommodate substantially higher traffic speeds than the old mountain road. Planners aimed to create a wide highway that unfamiliar motorists could navigate safely at approximately 60 miles per hour, requiring far more extensive earthmoving.

- Black Gore Creek was a major environmental constraint on the Vail Pass project. The creek supplied recreational reservoirs, contributed drinking water for Vail, and ultimately fed waters supporting valuable trout fishing downstream.

- The downstream trout fishery had received Gold Medal water designation. Protecting the creek therefore involved not only drinking water but also an important recreational and ecological resource.

- Vail Pass presented unusually difficult erosion and runoff conditions. Sandy soils, rapid late-spring snowmelt, and intense midsummer rainfall created substantial risks of sediment entering streams and water supplies.

- The National Environmental Policy Act of 1970 changed how interstate contractors approached construction. Contractors working on Vail Pass had to account for environmental impact assessments and pollution requirements alongside conventional engineering demands.

- Downstream officials were already concerned about sediment in the water supply before interstate construction began. Removing grass and other vegetation from slopes above the creek risked making an existing problem substantially worse.

- Contractors regularly tested creek water during construction to monitor sediment levels. The objective was to keep runoff-related pollution within acceptable limits and avoid environmental violations and potential fines.

- Hay bales, sandbags, and settling basins were used to control construction runoff. These measures slowed flowing water and allowed suspended soil particles to settle before runoff reached nearby streams.

- Temporary construction controls were insufficient for the highway's permanent drainage requirements. Engineers also had to design systems that would manage runoff and erosion throughout the road's operating life.

- Rapid revegetation of disturbed hillsides became a central erosion-control measure. Once the roadbed was established, contractors planted grasses and shrubs to stabilize exposed soil and reduce the amount washed away during rainfall.

- Highway designers commonly seek uphill cut slopes no steeper than 2:1. This means two units of horizontal distance for each unit of vertical rise, providing a more stable surface for vegetation and erosion control.

- Vail Pass adopted gentler cut slopes of approximately 2.5:1 or flatter wherever practical. The adjustment reflected the area's difficult soil, climate, and erosion conditions.

- Contractors used sprayed mulch and netting to help vegetation establish on steep slopes. These measures protected newly seeded surfaces and reduced the likelihood that rainfall would strip soil away before plants developed sufficient roots.

- Willows and strategically placed boulders were installed in natural drainage areas. They slowed flowing water, reduced erosion, and helped disturbed landscapes regain a more natural appearance.

- Roadside ditches and culverts redirected water around and beneath the interstate. Parallel ditches intercepted runoff traveling downhill toward the roadway and directed it to suitable drainage channels and culverts.

- Retaining walls replaced conventional earth embankments where filling would threaten Black Gore Creek or Tenmile Creek. These structures provided roadway support without allowing large volumes of fill to extend into sensitive waterways.

- Explosives were used to cut steep rock faces where ordinary excavation could not provide suitable road geometry. Engineers also used planted topsoil and protective netting above exposed cuts to reduce future rockfall hazards.

- Twenty-three separate sections of the Vail Pass interstate were constructed on bridges. Elevated structures helped the road cross unstable terrain rather than relying entirely on excavated mountainsides and earth embankments.

- The Vail Pass alignment was complicated by a fault line and historically active landslides. Much of the roadway between Vail and the pass crosses ground that has experienced continuing movement, making conventional roadbed construction especially difficult.

- The completed Vail Pass project incorporated an unusually broad range of highway engineering techniques. Cut-and-fill construction, exposed rock cuts, retaining walls, elevated bridges, drainage systems, and slope stabilization all became essential parts of the same mountain crossing.

- The 24-mile Vail Pass section was dedicated in 1978 at an estimated construction cost of $91 million. The narration gives an inflation-adjusted equivalent of approximately $427 million, or roughly $18 million per mile and $11 million per kilometer.

- The Vail Pass highway was deliberately designed to blend with its surrounding landscape. The aim was to make the interstate appear compatible with nearby forests, mountain scenery, ski resorts, and recreational areas rather than visually dominate them.

- Designers used reddish concrete to match local rock formations. Other visual measures included placing boulders in restored vegetation areas and shaping blasted rock faces to appear more natural.

- Some retaining walls were inspired by Frank Lloyd Wright's architectural style. Their appearance formed part of an intentional effort to integrate large highway structures with the mountain environment.

- The distinctive visual features of Vail Pass were eventually incorporated into planning guidance. Future modifications and additions were expected to respect the established landscape-sensitive design approach.

- I-70 requires continuous management because mountain conditions change after construction. Steep grades, sharp curves, winter weather, erosion, and shifting ground create risks that cannot be permanently eliminated through initial engineering.

- The Colorado Department of Transportation prioritizes highway locations where failures are especially dangerous or closures would be most disruptive. Limited resources require the agency to focus on vulnerable sections rather than treating every mile of the interstate equally.

- The Eisenhower Tunnel is one of I-70's most important traffic bottlenecks. Slower speeds through the tunnel produce substantial congestion even under ordinary operating conditions.

- Closing the Eisenhower Tunnel forces interstate traffic onto Loveland Pass. This diversion uses a winding and difficult two-lane mountain road that cannot efficiently accommodate normal interstate traffic volumes.

- The next shortest alternative to Loveland Pass adds approximately two hours of travel. This lack of practical substitutes makes keeping the Eisenhower Tunnel operational a major transportation priority.

- Trucks carrying hazardous materials are generally prohibited from using the Eisenhower Tunnel. Fuel tankers and vehicles transporting dangerous chemicals must normally use Loveland Pass instead.

- The hazardous-materials restriction is intended to prevent catastrophic tunnel fires or chemical incidents. A major tanker fire inside the enclosed tunnel could threaten motorists, damage essential structures, and potentially close the interstate for months or years.

- The Eisenhower Tunnel has its own fire department, but its remote location limits the response to a major hazardous-materials disaster. Additional emergency resources could take hours to arrive, making prevention particularly important.

- Loveland Pass remains open through winter partly because hazardous-materials trucks need an alternative crossing. CDOT plows the road to its summit near 12,000 feet, making it Colorado's highest year-round road according to the narration.

- The hazardous-materials diversion creates a separate safety problem for truck drivers. Tankers carrying fuel or chemicals must navigate steep, winding roads at high altitude during severe Colorado winter conditions.

- Trucking industry advocates argue that the tunnel restriction prioritizes ski commuters over truck-driver safety. Their objection is that protecting the tunnel transfers considerable risk onto drivers operating heavy vehicles over Loveland Pass.

- CDOT retained the hazardous-materials restriction after a feasibility study reconsidered the policy. The department concluded that the existing arrangement still provided the best overall balance of safety risks.

- The Eisenhower Tunnel corridor is also vulnerable to avalanches because of its high elevation and surrounding mountain slopes. Heavy snow can accumulate above the interstate on both sides of the Continental Divide.

- Mount Bethel contains recognizable avalanche paths near the highway. Tree-free corridors descending the mountainside reveal areas where snow has repeatedly traveled downhill.

- An uncontrolled avalanche could bury I-70 beneath snow and debris for hours or days. Such an event could trap or injure motorists while disrupting one of Colorado's most important transportation links.

- CDOT uses remotely operated avalanche-control devices to trigger smaller, managed slides. The narration identifies O'bellx-style devices positioned near the tops of avalanche paths on both sides of the Eisenhower Tunnel.

- The avalanche-control devices produce concussive blasts intended to release unstable snow. Their effectiveness depends on snow conditions, but controlled releases can reduce the amount of snow available for a larger natural avalanche.

- Controlled avalanches are initiated during planned highway closures, preferably at low-traffic periods. This allows crews to keep vehicles out of danger while reducing the risk of a major uncontrolled slide later.

- Glenwood Canyon has emerged as another exceptionally vulnerable section of I-70. Located approximately 80 minutes west of the Eisenhower Tunnel, the interstate follows the Colorado River through a narrow canyon bordered by walls approximately 1,000 feet high.

- Glenwood Canyon has no practical nearby diversion route when the interstate closes. A journey normally taking around 30 minutes can become a four-hour trip along rural two-lane roads.

- Major Glenwood Canyon closures can effectively separate Colorado's Western Slope from Denver. The consequences extend beyond local traffic because I-70 provides a critical connection between the state's eastern and western regions.

- A wildfire closed I-70 through Glenwood Canyon for 13 days in 2020. The fire created an immediate transportation disruption and left the surrounding slopes vulnerable to additional hazards.

- The wildfire destroyed vegetation that had stabilized the canyon's steep slopes. Without the roots holding soil in place, subsequent rainfall could generate major mudslides carrying earth and debris onto the interstate.

- Post-fire mudslides created a danger that could potentially bury both the roadway and motorists. These hazards persisted after the original wildfire, turning rainfall into a serious concern for highway operators.

- Unlike avalanches, mudslides cannot be deliberately triggered under controlled conditions to reduce future risk. CDOT consequently had to rely more heavily on forecasting, monitoring, and preventive closures.

- CDOT began closing the Glenwood Canyon section when heavy rainfall was forecast. Even the threat of a serious mudslide could temporarily sever the interstate connection, without any debris having reached the road.

- The highway's most serious operational risks change over time. Avalanche-prone mountain passes, tunnel traffic, wildfire damage, and mudslides have required CDOT to revise where it concentrates attention and resources.

- I-70 fundamentally changed Colorado's economic activity and settlement patterns. The interstate made cross-mountain travel more practical, connected previously difficult-to-reach communities, and supported the development of recreational destinations and regional commerce.

- The highway has become essential infrastructure despite once being considered an impractical engineering undertaking. Its economic importance and the lack of suitable alternative routes make continued operation and maintenance critical to Colorado.

- Decades after its original construction, I-70 requires major upgrades. The narration identifies aging infrastructure, changing transportation demands, and continuing environmental hazards as reasons for further investment.

- Federal infrastructure funding was supporting upgrades to the interstate at the time of the episode. The narrator referred to an approximately $1 trillion federal infrastructure package passed about two years earlier, indicating that new investment was being directed toward renewing transportation infrastructure.

- The federal infrastructure legislation was politically contentious despite funding practical transportation projects. The narrator described congressional and public opinion as strongly divided along party lines, with media coverage often emphasizing political winners and losers rather than the infrastructure work itself.