On Sunday morning, I got to cycle across the Esplanade Bridge and down Shenton Way with my family ("Cyclists and runners carefree on Car-Free Sunday"; March 28).

The open road - space ordinarily off limits to young or amateur cyclists - was briefly and delightfully ours. As my five-year-old pedalled along, he repeatedly exclaimed: "This is so awesome! This is great!"

I thank National Development Minister Lawrence Wong and the Urban Redevelopment Authority.

I encourage them to keep up this terrific public good, and expand it, if possible.

As a social psychologist who has been researching happiness for more than 15 years, I believe Car-Free Sundays have the potential to improve the happiness of the residents of Singapore, for several reasons.

First, empirical research has demonstrated that exposure to nature improves people's happiness.

The Car-Free route included the beautiful greenery of the Padang, while the journey across the Esplanade Bridge offered a spectacular view of Marina Bay.

On foot or bike, one takes in the full sensory experience, including the warm breeze and sunshine, and with plenty of time to enjoy it.

Second, numerous studies have shown that even mild to moderate physical activity improves not only temporary mood but also long-term well-being.

Exercise enhances the function of the dopamine and serotonin systems that are responsible for positive mood and emotion regulation.

Third, one of the most robust findings in happiness research is that social relationships are essential - in fact, they are key - to our well-being.

On Sunday, I saw folding-bike clubs, scooter clubs, unicycle clubs and scores of families coming together. Almost everyone there was with another person, and all the happier for it.

While I understand it is not free to operate Car-Free Sundays, the return on investment (in terms of the happiness of Singaporeans) will far outweigh the costs.

In fact, University of Virginia researchers have found that nations with high income inequality had lower levels of national happiness than those with low income inequality.

More importantly, the same researchers demonstrated that spending on public goods can mitigate this effect.

In short, Car-Free Sundays have an impact on the happiness of the people of Singapore.

I have already marked my calendar for the last Sunday of every month until July. I hope there will be many more.

Christie Napa Scollon (Dr)