ISABEL RUBIO ARROYO | Tungsteno

The world's most extreme roads are routes where engineering and risk go hand in hand. The Yungas Road in Bolivia, with its narrow stretches skirting sheer drop-offs, is among the best known for its extreme danger. China’s Tianmen Mountain Road climbs a mountainside via 99 hairpin bends carved directly into the rock. In the Indian Himalayas, high-altitude passes such as Khardung La, at over 5,300 metres, force drivers to contend with ice, fog, and landslides. In Canada, ice roads exist only in winter, crossing frozen lakes and endless tundra. In this article, we investigate which roads truly deserve the title of the world's most extreme.

“The Road of Death”

The North Yungas Road, known as the Road of Death, links La Paz in Bolivia with the subtropical Yungas valleys and the Amazon region. At just 64 km long and with a descent of 3,500 metres, the road has gained global notoriety due to its extreme danger. The highway is narrow, with sections barely three metres wide, and features tight bends, blind turns, and almost no guardrails. Drivers must contend with sheer drop-offs ranging from 400 to 1,000 metres, as well as dense fog, mud, and waterfalls that render the surface treacherously slippery. Some media outlets estimate that this road used to claim between 200 and 300 lives per year. Despite the risks, the road attracts some 25,000 visitors each year, including cyclists and motorcyclists, who willingly brave the potholes, traffic, and constant threat posed by the surrounding cliffs.

The North Yungas Road challenges drivers and cyclists with its narrow stretches. Credit: World Travel Guide

An “Avenue to the Heavens”

Tianmen Shan Big Gate Road, also known as the Avenue to the Heavens or the Road of 99 Curves, is located in Tianmen Mountain National Park in Hunan, China. This 11-kilometre route climbs from the foot of the mountain to Cave Square, reaching an altitude of around 1,100 metres. Due to its extremely tight hairpin turns, narrow sections running alongside precipices, and frequent fog, it is considered one of the most dangerous roads in the world. Given its proximity to the abyss and minimal margin for error, the route is only suitable for experienced drivers.

In recent years, however, it has also become a popular tourist destination and venue for cycling competitions and mountain races. Its dramatic landscape inspired James Cameron when designing the floating mountains in the Avatar films.

Tianmen Shan Big Gate in Zhangjiajie, China, is known as the Avenue to the Heavens. Credit: Travel and Home

One of the world’s most dangerous mountain passes

Khardung La, located in the Ladakh region of India, is one of the world’s most famous and challenging mountain passes. Rising to 5,359 metres (17,582 feet) above sea level, its extreme altitude exposes travellers to Acute Mountain Sickness (AMS). The road itself is narrow and slippery in places, with several sections in poor condition. Heavy traffic and military convoys can cause delays and increase the risk of accidents on the single lane sections. The pass is also subject to bad weather and geological hazards, such as avalanches, rockfalls, and heavy snowfall, and remains closed for several months each year. The remoteness of the area and poor logistics make the journey even more challenging.

There is no medical assistance available along the entire route, and facilities at the summit are extremely limited. In addition, its proximity to the borders with Pakistan and China results in a heavy military presence, and some travellers require a special permit to cross the pass.

There is usually a military presence at Khardung La. Credit: Vyacheslav Argenberg / Creative Commons.

A road built on ice

The Tibbitt to Contwoyto Winter Road, located in Canada’s Northwest Territories and Nunavut, is the longest heavy-haul ice road in the world. Spanning between 400 and 600 kilometres, it links Tibbitt Lake, near Yellowknife, with diamond mines such as Ekati, Diavik, and Gahcho Kué. It is a seasonal route, rebuilt every year starting in December, and is typically open from February to late March. Around 85% of the road runs over frozen lakes, while the remaining 15% crosses short stretches of permafrost peatland.

Despite being one of the best-managed and safest roads in North America due to strict monitoring and controls, it is still considered dangerous for several reasons. The ice must reach a minimum thickness of 74 centimetres for the road to open and 100 centimetres to support fully loaded trucks. Speed limits for loaded vehicles are restricted to 25 kilometres per hour. Drivers may encounter snowstorms, strong winds and near-zero visibility, and the journey itself can take between 14 and 18 hours in complete isolation. One of the greatest threats to this ice road is climate change, which can shorten the operating season or weaken the ice.

The Tibbitt to Contwoyto Winter Road depends entirely on the thickness of the ice. Credit: Steven TenHave

Tungsteno es un laboratorio periodístico que explora la esencia de la innovación.

El proyecto de ampliación de la Línea 8 del Metro de Barcelona añadirá cuatro kilómetros, tres nuevas estaciones (Gràcia, Clínic y Francesc Macià) y adecuará la actual estación de Espanya. La UTE responsable de las obras está formada por Sacyr (27,5%), Ferrovial (27,5%), Copcisa (22,5%) y Copisa (22,5%).

La tuneladora (TBM) encargada de construir esta ampliación se encuentra en Sant Boi, donde se están realizando las últimas pruebas. 

“Estamos llevando a cabo inspecciones detalladas, pruebas de componentes, software, automatización y funcionamiento mecánico para garantizar su correcto funcionamiento antes de moverla al pozo de ataque de la Gran Vía”, explica Toni Julià, jefe de Obra de la UTE.

 

Este mes se empezarán a trasladar los componentes de la tuneladora hacia el pozo de ataque, al punto en el que comenzará la excavación. Esta máquina moverá más de 300.000 metros cúbicos de tierra, que se extraerán por el parque Joan Miró mediante un microtúnel auxiliar construido en la calle Llançà. Una cinta conducirá los materiales sobrantes hasta los camiones que los trasladarán a vertedero.

“El pozo de ataque está muy avanzado: en la parte delantera se ejecuta la solera donde montaremos la tuneladora y en la trasera se prepara la hendidura para el entronque con el microtúnel. También estamos construyendo una nave acústica para minimizar el ruido durante la perforación”, añade Juliá.

Pantallas de 82 metros

Mientras avanza el montaje de la TBM, otros frentes de obra siguen a pleno rendimiento. En las estaciones de Hospital Clínic y Francesc Macià trabajan las hidrofresas ejecutando pantallas de hasta 82 metros de profundidad, las más profundas construidas hasta ahora en España. 

Estas pantallas permitirán excavar los pozos por los que pasará la tuneladora y, posteriormente, construir las cavernas que albergarán los andenes.

Datos clave de esta macro obra

“Con 19 millones de usuarios previstos al año, es una de las actuaciones con mayor rentabilidad social y económica del Plan Director de Infraestructuras de la Generalitat”, destaca Toni Julià.

La ampliación de la L8 conectará los dos grandes ramales ferroviarios de Barcelona —Baix Llobregat y Vallès— de la red de FGC, mejorando la intermodalidad y la movilidad en toda la ciudad. El proyecto cuenta con un presupuesto de 322 millones de euros y un plazo de ejecución de 61 meses.

Understanding the seabed is key before initiating any marine construction project. Bathymetry, or detailed seabed mapping, consistently faces numerous challenges, including the inherent conditions of the sea itself.

These challenges have arisen during the Central Pier Extension, Phase 2, project at the Port of Bilbao. There, we conducted verification tests to enable operations with easily transportable semi-submersible uncrewed vehicles.

"We have innovated by installing a multibeam echosounder and a side-scan sonar on these units. Using acoustic waves, we acquire seabed elevation data," explains Alfredo Pérez, Head of Marine Works at Sacyr Engineering and Infrastructure’s Technical Services Department. Pérez was recently honored with the Natural Innovators 2025 award, a Sacyr internal program for the promotion and advancement of innovation.

"Thanks to this drone, we reduce CO2 emissions and enhance operational capability in the most unfavorable weather conditions," he explains.
"Tests have been conducted both in the open sea and within the port basin. This allows for a more thorough evaluation of the characteristics of this semi-submersible unit and enables a comparison with conventional methods," Alfredo Pérez adds.

Acoustic probes are the only ones that propagate effectively in turbid aquatic environments. This high-frequency echosounder generates a conical beam, providing a data point cloud with far more comprehensive seabed information than traditional single-beam echosounders. This point cloud is then used for data processing, interpolation, and noise reduction, ultimately rendered as contour maps for detailed seabed interpretation.

Bathymetric surveys performed with this method are compared with those obtained by conventional means, and an analysis is conducted to determine if the tolerances between both datasets are within acceptable values.

The echosounder used in Bilbao offers a scan that allows for real-time visualization of the seabed. It provides insights into the terrain's hardness and roughness and performs side scans for object detection. Its measurements can be taken in environments up to four times more challenging than those supported by conventional methods.

"In the future, our goal is to expand the inner data cone to 160 degrees. We also plan to install an antenna on the echosounder to use an airborne bathymetric lidar, which would provide both terrestrial and marine data in a single operation. This way, we will have complete terrain profiles, overlapping both the marine and terrestrial sections," says Alfredo.

Mining and underground works involve the presence of crystalline silica, a naturally occurring mineral known to be carcinogenic. To address this risk, we have implemented a continuous, real-time monitoring system designed to protect the professionals working on our projects.

Royal Decree 1154/2020 classified Respirable Crystalline Silica (RCS) as a carcinogenic agent, significantly reinforcing employers’ obligations in the field of occupational health and safety. In addition, the General Regulations on Basic Mining Safety Standards require an accredited Administration Collaborating Entity (ECA) to take dust samples every four months at workstations where there is a risk of exposure.

Our Health and Safety Department has gone beyond regulatory requirements by deploying a mobile system for continuous, real-time silica monitoring: the AIR S Silica Monitor.

“Having access to real-time data raises awareness of RCS exposure for both workers and management,” explains David Barreda, Prevention Manager at Sacyr Engineering and Infrastructure in Northern Spain.

Crystalline silica is a very common mineral found in rocks, sand, and soil. It is present in construction materials such as concrete and brick, as well as in activities like mining, quarrying, and construction. When its fine dust particles are inhaled, respirable crystalline silica becomes a serious health hazard, increasing the risk of lung cancer, silicosis, and chronic obstructive pulmonary disease (COPD).

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The AIR S Silica Monitor was used during excavation works in the tunnels of the Access to the Outer Port of Langosteira project and will later be deployed during ballast spreading for track installation.

RCS levels can vary significantly depending on the stage of construction, with different exposure levels during blasting, debris removal, and drilling operations.

“This new system allows us to make informed decisions and continue reducing our employees’ exposure to RCS,” says David Barreda.

“The company is committed to protecting both our employees and our subcontractors. They value our concern for their health and the continuous control we maintain over the working environment,” he adds.

How the Monitor Works

The system analyzes multiple parameters in real time to detect RCS, including particle size, symmetry, and a range of unique optical markers characteristic of respirable crystalline silica particles.

At the same time, it uses optical refraction technology combined with light-scattering photometry, analyzing each sampled particle and classifying it according to its identifiable optical properties.

This approach allows the system to detect all forms of RCS — including alpha and beta quartz, cristobalite, and tridymite — across all relevant particle sizes within the respirable fraction.

The resulting data is combined with particle mass analysis to provide measurements in both mg/m³ and particles per liter.
Thanks to this comprehensive information, site management can make timely, well-informed decisions to ensure the safety of everyone working on the project.

We present the 2025 Innovation Report, a journey through everything we have been able to achieve together. Every project, every idea and every collaboration demonstrates that innovation is the driving force behind our drive to transform the world and meet our challenges.

During 2025, we allocated €8.2 million to the development of new solutions and launched 42 innovation projects. In addition, 40% of the initiatives had sustainability at their core, reaffirming our will to care for the planet as we move forward.

Innovation was also born of collaboration. Thanks to our commitment to Open Innovation, we developed 13 projects in alliance with startups, demonstrating that shared talent amplifies our capabilities and allows us to look further ahead.

Internal participation is also key. More than 2,700 professionals joined initiatives such as the 3 iFridays and 8 iPodcasts, spaces that inspire, connect and bring together new ways of thinking. And we celebrated the 10th edition of the Natural Innovators Awards, with 117 nominations from 11 countries, where we recognized the talent, creativity and innovative drive of 18 people.

With each step taken, we reinforce our commitment to a more efficient and sustainable infrastructure model with a positive impact on society and the environment. Innovation will continue to guide our roadmap and open up new opportunities to continue transforming the world we share.

Discover the 2025 Innovation Report here.