Integrating Shared Mobility Services with Transit Could Produce Economic and Environmental Benefits

This research brief summarizes the findings from the associated study, which examined the potential to improve transportation system efficiency by reevaluating and redefining the role of public transit and its design principles in the new context of technology and shared mobility. Specifically, it evaluated the financial feasibility of an integrative, multimodal transportation system where public and private mobility services coexist to maximize economic and environmental benefits and free up public transit resources to be reallocated more efficiently

Observational evidence for a metal rich atmosphere on the super-Earth GJ1214b

We report observations of two consecutive transits of the warm super-Earth exoplanet GJ1214b at 3.6 and 4.5 microns with the Infrared Array Camera instrument on-board the Spitzer Space Telescope. The two transit light curves allow for the determination of the transit parameters for this system. We find these paremeters to be consistent with the previously determined values and no evidence for transit timing variations. The main investigation consists of measuring the transit depths in each bandpass to constrain the planet's transmission spectrum. Fixing the system scale and impact parameters, we measure R_p/R_star=0.1176 (+0.0008/-0.0009) and 0.1163 (+0.0010/-0.0008) at 3.6 and 4.5 microns, respectively. Combining these data with the previously reported MEarth Observatory measurements in the red optical yields constraints on the GJ1214b's transmission spectrum and allows us to rule-out a cloud-free, solar composition (i.e., hydrogen-dominated) atmosphere at 4.5 sigma confidence. This independently confirms a recent finding that was based on a measurement of the planet's transmission spectrum using the VLT. The Spitzer, MEarth, and VLT observations together yield a remarkably flat transmission spectrum over the large wavelength domain spanned by the data. Consequently, cloud-free atmospheric models require more than 30% metals (assumed to be in the form of H2O by volume to be consistent with all the observations.Comment: Accepted for publication in ApJL. 13 pages, 3 figures, 1 tabl

Carbon Free Boston: Transportation Technical Report

Part of a series of reports that includes: Carbon Free Boston: Summary Report; Carbon Free Boston: Social Equity Report; Carbon Free Boston: Technical Summary; Carbon Free Boston: Buildings Technical Report; Carbon Free Boston: Waste Technical Report; Carbon Free Boston: Energy Technical Report; Carbon Free Boston: Offsets Technical ReportOVERVIEW: Transportation connects Boston’s workers, residents and tourists to their livelihoods, health care, education, recreation, culture, and other aspects of life quality. In cities, transit access is a critical factor determining upward mobility. Yet many urban transportation systems, including Boston’s, underserve some populations along one or more of those dimensions. Boston has the opportunity and means to expand mobility access to all residents, and at the same time reduce GHG emissions from transportation. This requires the transformation of the automobile-centric system that is fueled predominantly by gasoline and diesel fuel. The near elimination of fossil fuels—combined with more transit, walking, and biking—will curtail air pollution and crashes, and dramatically reduce the public health impact of transportation. The City embarks on this transition from a position of strength. Boston is consistently ranked as one of the most walkable and bikeable cities in the nation, and one in three commuters already take public transportation. There are three general strategies to reaching a carbon-neutral transportation system: • Shift trips out of automobiles to transit, biking, and walking;1 • Reduce automobile trips via land use planning that encourages denser development and affordable housing in transit-rich neighborhoods; • Shift most automobiles, trucks, buses, and trains to zero-GHG electricity. Even with Boston’s strong transit foundation, a carbon-neutral transportation system requires a wholesale change in Boston’s transportation culture. Success depends on the intelligent adoption of new technologies, influencing behavior with strong, equitable, and clearly articulated planning and investment, and effective collaboration with state and regional partners.Published versio

Time evolution and rotation of starspots on CoRoT-2 from the modelling of transit photometry

CoRoT-2, the second planet-hosting star discovered by the CoRoT satellite, is a young and active star. A total of 77 transits were observed for this system over a period of 135 days. Small modulations detected in the optical light curve of the planetary transits are used to study the position, size, intensity, and temporal evolution of the photospheric spots on the surface of the star that are occulted by the planetary disk. We apply a spot model to these variations and create a spot map of the stellar surface of CoRoT-2 within the transit band for every transit. From these maps, we estimate the stellar rotation period and obtain the longitudes of the spots in a reference frame rotating with the star. Moreover, the spots temporal evolution is determined. This model achieves a spatial resolution of 2\circ. Mapping of 392 spots vs. longitude indicates the presence of a region free of spots, close to the equator, reminiscent of the coronal holes observed on the Sun during periods of maximum activity. With this interpretation, the stellar rotation period within the transit latitudes of -14.\circ 6 \pm 10 \circ is found to be 4.48 days. This rotation period is shorter than the 4.54 days as derived from the out-of-transit light modulation. Since the transit data samples a region close to the stellar equator, while the period determined from out-of-transit data reflects the average rotation of the star, this is taken as an indication of a latitudinal differential rotation of about 3% or 0.042 rad/d.Comment: 8 pages, 12 figure

From Buses to BRT: Case Studies of Incremental BRT Projects in North America, MTI Report 09-13

Bus Rapid Transit (BRT) uses different combinations of techniques to improve service, such as bus-only lanes and roads, pre-boarding fare collection, transit priority at traffic signals, stylish vehicles with extra doors, bus stops that are more like light rail stations, and high frequency service. This study examines five approaches to BRT systems as implemented by public transit agencies in California, Oregon, and Ontario. The case studies as a group show that BRT can be thought of as a discretionary combination of elements that can be assembled in many different combinations over time. Every element incrementally adds to the quality or attractiveness of the service. This latitude provides transit agencies with many benefits, including the ability to match infrastructure with operating requirements. For example, a BRT service can combine operations serving free flowing arterial roads in the fringes of the downtown with dedicated lanes in areas closer to city center where congestion is greatest. Buses can operate both on and off the guide way, extending the corridors in which passengers are offered a one-seat ride with no transfer required. Transit agencies also can select specific BRT components and strategies, such as traffic signal priority and increased stop spacing, and apply them to existing local bus operations as a way to increase bus speeds and reduce operating costs. The specific elements selected for a BRT route can be implemented all at once, or in incremental stages either or both geographical extensions or additions of features. All of the case studies showed ridership improvements, but the Los Angeles Metro Rapid bus system illustrates the wide geographic coverage, improved ridership, and moderate cost per new rider that is possible with an approach that includes fewer BRT features spread over more miles of route. Quantitative results from the case studies suggest that incremental improvements, applied widely to regional bus networks, may be able to achieve significant benefits at a lower cost than substantial infrastructure investments focused upon just one or a few corridors

The Core Plan or How I Learned to Stop Worrying and Love the Central City: Shifting Control of Regional Mass Transit to the Central City

[Excerpt] “Mass transit in the United States is moribund: it plays a meaningful transportation role in only a handful of American regions. It is clear that the status quo—where state-created special-purpose districts (SPDs) provide limited regional mass transit options and new mass transit construction progresses at a glacial pace—is a colossal failure. This failure necessitates a new model of mass transit ownership and management. It is time for the region’s central city to own and operate the region’s mass transit system extraterritorially, free from significant control by the outer cities (the suburbs) and the state. This article calls this arrangement the “Core Plan.” The key advantages of the Core Plan are: (1) the re-politicization of the mass transit planning process via the heavily politicized central city, allowing the public to effectively express its policy desires while reinvigorating the mass transit debate; (2) the central city’s significant institutional competence concerning regional transportation operations, as shown by the central city’s ownership of large international airports and systems of airports that serve entire regions; and (3) the faster pace at which the central city will be able to build mass transit versus the status quo of SPDs. The Core Plan reflects and integrates the United States’ long history of municipal extraterritorial powers, where cities own property and operate businesses beyond their territorial limits, including regional transportation operations (international airports). The Core Plan returns power over the region’s mass transit to the local level, while dramatically speeding up the mass transit construction and integration process.

The downtown parking syndrome: does curing the illness kill the patient?

Consumers and businesses alike cite the lack of free parking as one of the major problems associated with working, playing, and shopping downtown. A shortage of parking spaces can also lead to higher prices for those parking slots available as well as violation of parking ordinances by frustrated citizens. In light of widespread concerns about parking downtown, should large cities adopt policies to encourage more parking in a central business district (CBD), or should they improve public transit as an alternative to driving? Cities must consider many factors before answering such questions. Effective parking policies must strike a balance between convenient parking and maintenance of the dense urban fabric that makes the CBD uniqueCities and towns ; Local transit ; Philadelphia (Pa.)

Transmission spectroscopy of the sodium 'D' doublet in WASP-17b with the VLT

The detection of increased sodium absorption during primary transit implies the presence of an atmosphere around an extrasolar planet, and enables us to infer the structure of this atmosphere. Sodium has only been detected in the atmospheres of two planets to date - HD189733b and HD209458b. WASP-17b is the least dense planet currently known. It has a radius approximately twice that of Jupiter and orbits an F6-type star. The transit signal is expected to be about five times larger than that observed in HD209458b. We obtained 24 spectra with the GIRAFFE spectrograph on the VLT, eight during transit. The integrated flux in the sodium doublet at wavelengths 5889.95 and 5895.92 {\AA} was measured at bandwidths 0.75, 1.5, 3.0, 4.0, 5.0, and 6.0 {\AA}. We find a transit depth of 0.55 \pm 0.13 per cent at 1.5 {\AA}. This suggests that, like HD209458b, WASP-17b has an atmosphere depleted in sodium compared to models for a cloud-free atmosphere with solar sodium abundance. We observe a sharp cut-off in sodium absorption between 3.0 and 4.0 {\AA} which may indicate a layer of clouds high in the atmosphere.Comment: Amended for typographic conventions following publicatio