Every four years, the American Society of Civil Engineers issues a report card on the condition of the nation's infrastructure. In 2013, the last year a report was released, the country received a sad D+ – something that candidate Donald Trump highlighted during his presidential campaign. (See also: Build Your Portfolio With Infrastructure Investments.)

Now, as president, Trump has promised $550 billion in spending to spruce up the nation's crumbling infrastructure, a prospect that should encourage investors who seek exposure to this niche. (See also: How Big Investors Will Profit From Trump's Infrastructure Bonanza.)

It is important to note that infrastructure is an extremely broad category, encompassing transportation, communications, water and electricity – representing hundreds, if not thousands, of equities. Selection is essential to success, since not all "infrastructure" stocks will take off under the proposed spending. (See also: Democrats Propose $1 Trillion Infrastructure Plan.)

That being said, well diversified companies positioned to handle major infrastructure projects should do well over the medium- to long-term, especially if the administration follows through with its spending commitment. Here's a look at four of the most promising infrastructure stocks.

1. AECOM (ACM)

AECOM's business is designing, financing, building and operating infrastructure assets for federal and state governments and businesses. With a market cap of just under $6 billion and fiscal 2016 annual revenue of $17.47 billion, the company is well-positioned to handle a large influx of new government projects.

The company recently merged with rival URS to enhance its focus on the energy and transportation sectors, areas that are sure to see new spending under the Trump administration. In fact, AECOM stock surged sharply on Trump's victory, rising from $27.61 on Nov. 8, 2016, to $37.54 a week later, reaching a high of over $40 in December 2016. As of Feb. 13, 2017, the stock was trading at around $38, equating to a 55% increase over the past year. The stock has a median 12-month price target of $43.50 and a consensus rating of Outperform. (See also: Heavy Construction Stocks Leading the Market Higher.)

2. Vulcan Materials Company (VMC)

"Construction aggregate" sounds like a boring business, but these little bits of gravel, limestone and sand form the foundation of all sorts of building projects, including high-priority infrastructure items such as bridges, roads and industrial plants. Vulcan is the largest producer of these construction products, and it estimates that 75% of the population growth in the coming years will take place in states currently served by the company.

Vulcan has a market cap of $16.2 billion and generated annual revenue of $3.59 billion in 2016, which equates to a revenue growth rate of nearly 9% year over year. As of Feb. 13, the stock was trading at $122.46, a one-year increase of 33.08%. Its median price target is $141.50, and the consensus forecast is Outperform.

3. Caterpillar Inc. (CAT)

You can't build infrastructure without heavy construction equipment, and Caterpillar is a big name in massive earth-moving machines. Caterpillar had been on a slow slide over recent years, but 2016 saw the beginning of a recovery as the company implemented strict cost-cutting measures. With new infrastructure spending on the table, Caterpillar is well positioned to profit handsomely given its enhanced cost control. Two mergers and acquisitions in 2016 (Kemper Valve & Fittings and M2M Data Corp.) also boosted Caterpillar's stock price.

Caterpillar has a market cap of $56.3 billion and posted annual revenue of $38.5 billion in 2016, down 12% from 2015 primarily due to a slowdown in construction in China. However, the stock is up 56% over the past 12 months, trading at $98.50 on Feb. 13, above its 12-month median price target of $96.50 and $23.50 off its Street-high price target of $122 per share. (See also: Caterpillar Headed Into 2017 Cross-Currents.)

4. Quanta Services, Inc. (PWR)

Quanta is a specialty contractor providing infrastructure services primarily to the oil and gas and electrical power industries, all of which stand to benefit under Trump's infrastructure spending plans. Quanta is also a prime provider of oil and gas pipelines and renewable energy infrastructure, including onshore and inland hydroelectric projects.

Quanta has a market cap of $5.59 billion and posted annual revenue of $7.54 billion in 2015, up nearly 14% over the previous year. As of Feb. 13, the stock was trading at $37.15, up 112% over the previous 12 months and near its average 12-month price target of $39. (See also: Hidden Buying Pressure Lifting These S&P 500 Stocks.)

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