Despite hybrid-electric vehicles becoming more prominent in the on-road light-duty vehicle fleet, few studies have evaluated their real-world particle emissions. Hot-stabilized tailpipe particle number concentrations, emission rates, and number distributions emitted from two 2010 Toyota Camry vehicles—one hybrid and one conventional—were quantified during city driving in Burlington, Vermont, at ambient temperatures between −5°C and 9°C with the University of Vermont total onboard tailpipe emissions measurement system. Across replicate real-world runs, the average total cumulative particle number (3- to 3,000-nm particle diameter) emission rates measured for the hybrid vehicle were two times higher than that of the conventional vehicle, despite the hybrid vehicle's internal combustion engine being off 16% to 57% of the run duration. Average second-by-second number distributions for the conventional vehicle had three particle modes (10, 50, and 400 nm), whereas the broader hybrid vehicle distributions had two distinct modes (50 and 400 nm) with shoulders at 10 and 20 nm. These distributions changed little over the route for a given vehicle type. The unexpected higher particle number emission rates from the hybrid, and possibly the differences in number distributions, may be explained by an observed pattern of internal combustion engine restarts under stop-and-go driving that resulted in extreme particle emission rates up to 3.5 × 1010 (number per second) at every engine restart. The hybrid restart behavior resulted in high particle number emissions localized primarily at intersections. More detailed study is needed on different hybrid vehicle designs to determine the broader significance of the observed particle emission patterns.

Vehicle emissions during cold start are known to be significantly higher than after optimal vehicle operating temperatures are reached. There are limited data, however, on particle number and size distributions during cold start. Cold-start tailpipe emissions from a 1999 Toyota Sienna minivan were quantified at ambient temperatures between 20°C and 37°C using a novel system, the total onboard tailpipe emissions measurement system (TOTEMS), assembled to quantify the full suite of exhaust emissions from light-duty vehicles. TOTEMS particle number distributions were measured from 5.6 to 562 nm using an engine exhaust particle sizer (EEPS) and total 3- to 3,000-nm particle counts were measured using an ultrafine condensation particle counter (UCPC) with 1-s temporal resolution during cold start and warm-up driving. Second-by-second particle number distributions from five cold-start emissions tests showed similar particle emissions patterns, allowing for three different cold-start phases to be identified based on particle number emissions behavior. Cold-start duration ranged from 165 to 230 s and increased with decreasing ambient temperature. Different particle sizes during each phase were emitted for different lengths of time, with the most abundant particles in the nanoparticle (diameter <50 nm) range. The mean particle number distributions showed more than 99% of total particle number below 100 nm. Concentrations of ultrafine particles (<100 nm) during cold start were at least 10 to 100 times (EEPS), and as much as 1,000 times (UCPC), above hot-stabilized idle emissions. Observations also suggest the presence of tiny particles below 6 nm during cold start.

Tailpipe pollutants from motor vehicles are linked to environmental concerns and human health issues. Gasoline engine ignition produces a significant portion of trip emissions, but few studies have quantified mobile source air toxic (MSAT) species for light-duty vehicles during cold start. Real-world tailpipe emissions were measured from a 1999 Toyota Sienna minivan with the University of Vermont total onboard tailpipe emissions measurement system. A Fourier transform infrared spectrometer measured 27 gas-phase emissions for cold start, extended idle, and warm-up driving at 1-s temporal resolution. Analysis demonstrated that (a) time to optimal function of emissions control devices was not indicated by one species, but varied for different pollutants; (b) extended idling after cold start produced elevated emissions for MSAT species as compared to warm-up driving; and (c) ambient temperatures ranging from 9.5°C to 38.4°C affected species from each emission category, with the exception of carbon dioxide. Carbon monoxide produced peak emissions three orders of magnitude higher than hot-stabilized conditions for an average of 90 s, regardless of operating conditions, while nitric oxide peak emissions were over an order of magnitude higher during warm-up driving than extended idle. Peak MSAT emissions, up to two orders of magnitude higher than hot-stabilized idle, were maintained or increased during extended idle and decreased to baseline within 100 to 200 s of warm-up driving. Results indicate extended idling after cold starts prolongs elevated concentrations of MSAT emissions, suggesting that recent policy efforts to reduce vehicle idling behavior could limit potential human exposure to the toxic exhaust constituents.

Road TypeCharacter NA City, Highway and Arterial ROAD Group Character NA Freeway Rural and Urban (combines Urban I and Urban II of "Road_Section") Facility & Vehicle Character NA concatenates Road Type and Vehicle Linkname Character NA Name of road with number to denote links between intersections (signalized or not) REC_CHAINAGE Continuous meters Number of meters along driving route REC_GRADE Continuous % road grade as measured by ARAN van, interpolated and infilled based on vehicle heading Fuel Consumption (mL/sec) Continuous mL/sec Volumetric fuel consumption rate in mL/sec Grade_percent Continuous % Road grade as measured by ARAN van, interpolated and infilled based on vehicle heading Grade_Bin Categorical (Nominal) % Bins of 1 % based on rounding Grade_percent E_CO2_gPsec Continuous g/sec Emission rate of CO2 in grams per second PNER_numberPsec Continuous #/sec Particle number emission rate (PNER) in number of particles per second, based on sum of EEPS channels (5.6-562 nm)

The TransitCenter Equity Dashboard tracks how well public transit systems in seven densely populated urban regions in the United States serve their riders and how changes to transit service affect riders over space, time, and cost constraints. The dashboard presents a series of charts and interactive maps that can be used to evaluate variations in transit accessibility and equity. It was created using publicly available data and primarily open-source software. All measures can be accessed by users seeking to conduct their own analyses. Results demonstrate differences in agency responses to COVID-19 as well as baseline transit service levels provided to different demographic groups.