...and this (4) (a)   (show) to be directly linked to the level of vehicle emissions from private cars (see, for example, Rivera, 1985; Maslin 1990; or Sharpe, 1994).

Due to the fact that urban transport policy in the UK is designed to reduce or discourage the use of private cars, there (5) (a)   (be) an increase in the sale of non-polluting vehicles such as the SPPPV (Single-Person Pedal-Powered Vehicle).

However, although the number of SPPPV users (6) (a)   (increase), safety and comfort issues need to be addressed if the number of users is to increase to a level at which a significant effect on environmental pollution can be achieved.

Researchers (7)  (a)   (study) and improved many aspects of the SPPPV.

In 1980, Wang et al. (8) (a)   (respond) to the need for increased safety by designing an SPPPV surrounded by a ‘cage’ of safety bars, ...

... and in 2001 Martinez (9) (a)   (develop) this further with the introduction of a reinforced polymer screen, which could be fitted to the safety bars to protect the cyclist’s face in the event of a collision.

The issue of comfort has also been addressed by many design teams;  in 1998 Kohl et al. (10) (a)   (introduce) an SPPPV with a built-in umbrella, which could be opened at the touch of a button, ...

... and more recently, Martinez (11) (a)   (add) a mesh filter, ...

... which can (12) (a)     (place) over the entire cage to reduce the risk of environmental pollution.

However, the resulting ‘cage’ or cover (13) (a)   (be) aerodynamically ineffective due to the shape of the umbrella and the weight of the mesh filter.

            In this study, we (15) (a)   (use) computer simulation to model the aerodynamic effect of the existing safety and comfort features...

...and we (16) (a)   (present) a new design...

...which (17) (a)   (integrate) these features in an optimally-effective aerodynamic shape.