Publications·March 14, 2024
This knowledge product—co-developed by the Asian Transport Outlook (ATO) and Clean Air Asia—asks whether Asia is actually bending the curve on transport-related air pollution. It weaves ATO’s 51-economy dataset (~650 indicators) with literature and policy scans to track emissions trends, health burdens, and the policy/technology mix now in play. The topline: progress is real but uneven—especially across income groups, sub-modes, and pollutant types—and the next gains hinge on closing NOx gaps, reining in shipping emissions, cleaning up used-vehicle flows, and scaling e-mobility without neglecting demand-side measures and public transport.
What’s driving transport emissions—and where decoupling shows up
Transport emissions ride on four intertwined drivers: GDP, vehicle ownership, transport activity (passenger-km/tonne-km), and infrastructure build-out. All four grew strongly, yet signs of decoupling emerged in the last decade as cleaner fuels/standards and targeted policies tempered air-pollutant growth relative to demand—though regional aggregates are skewed by a few large economies and country performance varies widely.
Using EDGAR as a common baseline, the report shows that since 1990 the transport sector’s PM₁₀ rose ~62%, NOx ~28%, SOx ~10%, while black carbon (BC) rose ~9%. Mode shares matter: historically, road dominated PM and NOx, but domestic waterways and inland shipping have become faster-growing contributors; data gaps for those sub-modes remain significant.
A dominant source with a declining growth rate
Asia–Pacific still accounts for a large slice of global road-transport emissions—about 33% (PM₁₀), 41% (NOx) and 19% (SOx) in 2018. Yet since 2000, tighter road standards and fuels have flipped the trajectory: between 2000–2015 road PM₁₀ growth fell to roughly −3%/yr (and NOx ~0%/yr); after 2015, with SDGs as a policy frame, the declines accelerated (road PM and NOx about −5%/yr and −1%/yr, respectively)—the sharpest improvement among world regions.
Uneven progress across income groups and pollutants
High-income economies show steady declines since 1990 across PM, BC, NOx, and SOx. Upper-middle-income countries slowed emission growth after 2000 and posted clearer drops post-2010. Low/lower-middle-income countries cut PM₁₀ and SOx, but NOx remains stubborn—because the largest NOx cuts materialize only with Euro IV and later levels (and with compliant fuels, inspection/maintenance, and real-world controls).
Health toll: diesel and shipping loom large, evidence is thin on quantified benefits
Traffic-related air pollution is a major health risk. Diesel vehicles account for a disproportionate share of the road disease burden (ICCT estimates ~72% of road TRAP burden), while shipping (ports + international) is linked to a sizable global mortality slice; Asia’s port megaregions amplify exposure. Despite this, few Asian studies quantify health co-benefits of transport policies: among 2000–2020 publications, only 53 reported traffic-related pollution effects and just 4 reported health impacts—an evidence gap that weakens benefit–cost cases for clean-transport measures.
What’s working: standards, fuels, and (some) enforcement
Two decades of vehicle-emission standards plus fuel-sulfur cuts have been decisive for new vehicles. In 2010, only ~9% of the Asia fleet was in countries at Euro 4+ with matching fuels; by 2023, that share reached ~93%. Caveats: the effect lags as fleets turn over, progress is slower for HDVs and 2-wheelers in some economies, standard-setting has stagnated in places, and success depends on 10–50 ppm sulfur fuels and I&M compliance.
The hard bits: used-vehicle trade, demand, and non-road modes
Used-vehicle flows can undermine gains where import regimes are lax. Asia imported nearly US$180B in new+used vehicles (2022). Countries are experimenting with bans/restrictions, age or mileage caps, emissions-based taxes, and pre/post inspections (e.g., India: ban + Euro VI for new; Thailand: used truck/bus bans; Sri Lanka/Fiji: tight age caps; Singapore: CEVS rebates/surcharges). Harmonized rules could prevent “dirty-fleet dumping.”
On the avoid side, policy moves exist but remain politically tough. The region spent ~US$590B on transport fossil-fuel subsidies (2010–2015) but cut that by more than half (2016–2021). Ownership caps, parking pricing and access restrictions are emerging (e.g., Bhutan, Nepal, Viet Nam intentions), yet broad-based demand restraint is still rare.
Shift and improve: mass transit, freight, and electrification
Asia built transit at massive scale in the last decade: ~66% of global added railway-km and ~72% of rapid transit (BRT/metro/LRT) occurred here—though on a per-capita basis infrastructure remains limited, and only 23/51 economies have modal-share targets embedded in national strategies (e.g., Malaysia 40% PT by 2030; Pakistan rail freight shift; Philippines cycling household target).
E-mobility is surging: ~77% of the global EV stock is in Asia, and ~94% of Asia’s EV sales are 2-/3-wheelers—a critical, affordable wedge for urban PM/NOx. 28/51 economies now have e-mobility targets (covering manufacturing, sales, fleets, and infrastructure). Electricity still provides only ~2% of transport energy today, but could double by 2030; many countries are crossing the 5% sales “tipping point.”
Railways are over 50% electrified region-wide (tracks), dominated by China, India, and the Russian Federation. Air-pollution reductions from rail electrification will grow as grids decarbonize: grid intensity worsened 2000–2015, but has been declining since 2015.
Domestic shipping/inland waterways energy use is climbing quickly; the sector historically burned high-sulfur fuels. IMO MARPOL Annex VI sulfur limits and early LNG transitions are helping, but data for domestic fleets are thin and PM/NOx controls remain a priority. Several Asian countries (e.g., ROK, Singapore, Japan, China, Philippines, Viet Nam) have ratified and begun implementing 0.5% sulfur requirements; broader ECAs and enforcement can accelerate gains.
Finance and implementation
Since 2000, Asia has invested about 2.4% of GDP in surface transport infrastructure. Roads still dominate spend, but the share for urban & heavy rail is inching up. Transport PPPs and climate bonds remain a small but growing slice of total transport finance. The report argues that aligning investment with co-benefits (safety, congestion, air, climate) can unlock more capital.
The through-line: co-benefits matter—but quantify them
Policy ambition and co-benefit framing are rising across Asia (more measures referencing air + climate together), yet quantified health benefits are seldom included in ex-ante or ex-post assessments. Building a stronger evidence base—with disaggregated emissions by sub-mode, better activity data for shipping, and health-impact quantification—would make cleaner-transport investments easier to defend and scale.
Bottom line: Asia has bent the road-transport pollution curve via cleaner fuels and vehicle standards, and it is rapidly scaling transit and electrification (especially 2-/3-wheelers). To sustain momentum, countries need to (i) push Euro IV+ or equivalent across all modes (including HDVs and 2Ws), (ii) fix used-vehicle leakages and I&M enforcement, (iii) target shipping and rail with fuel/tech + grid decarbonization, (iv) invest for modal shift and demand management, and (v) measure the health co-benefits rigorously to lock in public and political support.
Keywords
Asian Transport Outlook (ATO); Clean Air Asia; EDGAR emissions; PM₁₀; PM₂.₅; NOx; SOx; black carbon (BC); road/rail/navigation/aviation mode shares; Euro 4+ standards; fuel sulfur 50/10 ppm; inspection & maintenance (I&M); used-vehicle import restrictions; fossil-fuel subsidy reform; modal shift (BRT/metro/LRT, rail freight); e-mobility (2-/3-wheelers); railway electrification; MARPOL Annex VI (0.5% sulfur); LNG in domestic shipping; PPPs & climate bonds; co-benefits and health impact quantification.