The Malaysian states of Sarawak and Sabah are in the midst of building more than 2,000 kilometers (1,200 miles) of the Pan Borneo Highway.The goal is to boost the states’ economies and connect them with the Indonesian provinces on the island of Borneo as part of the Trans Borneo Highway.Advocates of the highway, including many politicians, say the upgraded, widened and in some places entirely new stretches of highway will link markets and provide a jolt to the promising tourism sector in Malaysian Borneo.But skeptics, including scientists and conservationists, argue that parts of the highway cut through ecologically sensitive areas and that planning prior to construction didn’t adequately account for the damage that construction could cause. This is the first article in our six-part series “Traveling the Pan Borneo Highway.” MIRI, Malaysia — Tucked under the sweep of green that blankets parts of Malaysian Borneo is a unique mix of nature, culture and outdoor adventures matched by few other places in the world. It’s true that in recent decades the country’s two states on the island, Sabah and Sarawak, have suffered significant deforestation, largely for timber and oil palm. But in a single week, a visitor can still scuba dive in the Celebes Sea, camp with Penan hunter-gatherers in the Baram River watershed, boat along the wildlife-rich Kinabatangan River, and trek through untouched primeval forests in Danum Valley and Maliau Basin. But despite those attractions, the tourism industry in these states “has not really flourished,” Malaysia’s federal works minister, Baru Bian, told Mongabay. A stork-billed kingfisher (Pelargopsis capensis) along the Kinabatangan River in Sabah. Image by John C. Cannon/Mongabay. Baru sees the lack of “connectivity” between these sites as a brake on both the development of tourism and broader expansion of Borneo’s economies. And judging by the funding that politicians earmarked for the Pan Borneo Highway early in the project’s development — some 27 billion ringgit, or about $6.4 billion — Baru is not alone in his belief that the lack of roads is holding these states back. In 2013, Najib Razak, Malaysia’s prime minister at the time, revived a long-nurtured plan for a Pan Borneo Highway that would connect the two states. The goal at the time was to build more than 2,000 kilometers (1,200 miles) of mostly divided four-lane highway by 2021 to spur a scale-up of tourism and other economic activities. Current projections put the final completion date in 2025. It would also link up with the Trans Borneo Highway, connecting Malaysian Borneo to the Indonesian provinces and Brunei on the world’s third-largest island, with more than 5,000 kilometers (3,100 miles) of roadway.